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s 

Bulletin  260  November,  1924       ^^  ^  ^ 

CONNECTICyi 
ACmCOLTURAL  EXPERIMENT  STATION 

NEW  HAVEN,  CONN. 


Rust  Infection  of  Leaves  in 
Petri  Dishes 


G.  P.  CLINTON 

and 

FLORENCE  A.   McCORMICK 


BOTANICAL   DEPARTMENT 


The  Bulletins  of  this  Station  are  mailed  free  to  citizens  of  Connecticut 
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CONNECTICUT  AGRICULTURAL  EXPERIMENT  STATION 

OFFICERS  AND  STAFF 
November,  1924. 


BOARD  OF  CONTROL. 
His  Excellency,  Charles  A.  Templeton,  ex-officio,  President. 

George  A.  Hopson,  Secretary Mount  Carmel 

Wni.  L.  Slate,  Jr.,  Director  and  Treasurer New  Haven 

Joseph  W.  Alsop Avon 

Charles  R.  Treat Orange 

Elijah  Rogers Southington 

Edward  C.  Schneider Middletown 

Francis  F.  Lincoln Cheshire 

STAFF. 
E.  H.  Jenkins,  Ph.D.,  Director  Emeritus. 

Administration.  Wm.  L.  Slate,  Jr.,  B.Sc,  Director  and  Treasurer. 

Miss  L.  M.  Brautlecht,  Bookkeeper  and  Librarian. 
Miss  J.  V.  Bergbr,  Stenographer  and  Bookkeeper. 
Miss  Mart  Bradley,  Secretary. 
William  Veitch,  In  Charge  of  Buildings  and  Grounds. 


Chemistry : 
Analytical 
Laboratory. 


E.  M.  Bailet,  Ph.D.,  Chemist  in  Charge. 
R.  E.  Andrew,  M.A.  1 

Owen  L.  Nolan  (     Assistant  Chemists. 

Harry  J.  Fisher,  A.B.      J 

Fr.^nk  C.  Sheldon,  Laboratory  Assistant. 

V.  L.  Churchill,  Sampling  Agent. 

Miss  Mabel  Bacon,  Stenographer. 


Biochemical 
Laboratory. 

Botany. 


T.  B.  Osborne,  Ph.D.,  Sc.D.,  Chemist  in  Charge. 


G.  P.  Clinton,  Sc.D.,  Botanist  in  Charge. 

E.  M.  Stoddard,  B.S.,  Pomologist. 

Miss  Florence  A.  McCormick,  Ph.D.,  Pathologist. 

Willis  R.  Hunt,  M.S.,  Graduate  Assistant. 

G.  E.  Graham,  General  Assistant. 

Mrs.  W.  W.  Kelsey,  Secretary. 


Entomology. 


W.  E.  Britton,  Pn-D., Entomologist  in  Charge;  State  Entomologist 

B.  H.  Walden,  B.Agr.       1 

M.  P.  Zappe,  B.S.  [     Assistant  Entomologists. 

Philip  Garman,  Ph.D.      J 

Roger  B.  Friend,  B.S.,  Graduate  Assistant. 

John  T.  Ashworth,  Deputy  in  Charge  of  Gipsy  Moth  Work. 

R.  C.  BoTSFORD,  Deputy  in  Charge  of  Mosquito  Elimination. 

Miss  Gladys  M.  Finley,  Stenographer. 


Forestry. 


Walter  O.  Filley,  Forester  in  Charge. 
A.  E.  Moss,  M.F.,  Assistant  Forester. 
H.  W.  E[icocK,  M.F.,  Assistant  Forester. 
Miss  Pauline  A.  Merchant,  Stenographer. 


Plant  Breeding. 


Donald  F.  Jones,  S.D.,  Geneticist  in  Charge. 
P.  C.  Mangelsdorf,  M.S.,  Graduate  Assistant. 


Soil  Research. 


M.  F.  Morgan,  M.S.,  Investigator- 


Tobacco    Sub-station    N.  T.  Nelson,  Ph.D.,  Plant  Physiologist. 

at  Windsor. 


Ths  Wilson  H.  Lee  Co. 


PLATE  XXV 


a.     II   stage    of     Phragmidium    Potentillae        b.     Ill    stage    of    Gijmnocoyiia 
on  Potentilla  canadensis,  Inf.  No.  1014a  II.  inter stitialis    on    Ruhus 

villosus,  Inf.  No.  959. 


d.     II   stage   of    Crouartium  ribicola 
on  Ribes  vulgar e,  Inf.  No.  764. 


c.  O  stage  of  G ymnosporangium 
Juniperi-virginianae  on 
Pyrus  Malus,  Inf.  No.  937. 


ARTIFICIAL  INFECTIONS  OF  RUSTS  IN  PETRI   DISHES. 


Rust  Infection  of  Leaves  in  Petri  Dishes.* 

G.  P.  Clinton  and  Florence  A.  McCormick. 


HISTORICAL. 


.On  May  21,  1918,  the  writers  placed  aeciospores  (Inf.  No.  298) 
of  Cronartium  rihicola  from  Pinus  Strohus  on  leaves  of  Rihes 
nigrum  in  a  Petri  dish  in  the  hope  of  determining  the  method  by 
which  the  germ  tubes  entered  the  leaves.  Within  twenty-four 
hours  it  was  found  that  they  had  gained  entrance  into  the  leaves 
through  thfe  stomates  and  the  dish  was  set  aside  for  later  examina- 
tion to  see  if  further  development  took  place.  About  ten  days 
after  inoculation  examination  showed,  much  to  our  delight, 
numerous  mature  uredinia.  Similar  inoculations  made  a  day  or 
two  later  showed  about  this  time  even  more  abundant  infections, 
in  fact  better  than  those  obtained  on  living  plants. 

These  results  encouraged  us  in  the  belief  that  this  method  of 
inoculation  might  possess  advantages  superior  to  that  with  living 
plants  in  the  greenhouse;  consequently  more  inoculations  were 
made  on  a  variety  of  Rihes  leaves  in  Petri  dishes.  Fair  success 
attended  these  experiments  although  the  inoculating  material 
used  was  not  very  good.  Improvement  of  the  methods  used  and 
comparison  of  Petri  dish  versus  pot  infections,  made  under  similar 
conditions  and  at  various  times,  finally  led  us  to  the  conclusion 
that  the  Petri  dish  method  gave  results  on  the  whole  equal  to  the 
pot  method  and  had  several  distinct  advantages  in  simplicity  of 
operation. 

Literature.  The  writers  made  brief  mention  of  this  method  in 
Bull.  2,  White  Pine  Blister  Rust  Control,  p.  14,  published  by  the 
American  Plant  Pest  Committee  in  1918  and  in  publications  of 
this  Station  (Bull.  214,  pp.  437,  440,  and  Bull.  222,  p.  471.)  in  1919 
and  1920. 

So  far  as  we  know  no  other  writers  have  published  statements 
concerning  successful  production  of  rust  sori  on  leaves  in  Petri 
dishes,  though  somewhat  similar  experiments  have  been  published 
by  various  workers.  For  instance  Farlow  (American  Acad.  Arts 
&  Sci.  20:  311.)  in  1885,  working  with  five  species  of  Gymno- 
syorangium,  produced  pycnia  on  detached  leaves  of  Crataegus  and 
Amelanchier  with  three  of  the  species  under  the  conditions  quoted 
as  follows:  ''The leaves  (Pomacese)  were  placed  on  moistened  glass 
slides  and  arranged  on  zinc  stands  under  bell-glasses.    The  sporidia 

*  This  paper  was  largely  written  in  the  spring  of  1921  when  other 
work  prevented  its  completion.  It  has  now  been  brought  up  to  date 
including  the  inoculations  made  since  then.  W«e  are  indebted  to  E.  M. 
Stoddard  of  this  department  for  the  photographs  used. 


476  CONNECTICUT    EXPERIMENT   STATION.  BULLETIN   260. 

were  then  carefully  dropped  upon  the  leaves,  which  were  immedi- 
ately covered  by  a  bell-glass.  The  leaves  under  each  glass  were 
sown  with  the  sporidia  of  but  one  species,  the  bell-glasses  were 
removed  for  a  moment  only,  and  at  no  time  were  the  leaves  under 
more  than  one  bell-glass  exposed.  I  also  used  a  number  of  small 
seedlings  of  Pomaceae,  each  pot  being  covered  by  a  glass  receiver." 

Ward  (Proc.  Roy.  Soc.  Lond.  69:  451.)  in  1902  described  a 
unique  method  for  growing  grass  seedlings  in  large  special  test 
tubes  where  pure  cultures  of  rusts  were  grown  on  them  while  thus 
protected.  His  method  is  best  described  by  the  following  extracts 
from  his  paper:  "In  order  to  obtain  more  decisive  answers  to 
such  questions  as — Are  any  of  the  results  obtained  on  plants  in  the 
open  or  merely  covered  with  bell-jars  and  so  forth,  due  to  spores 
accidentally  introduced,  or  to  mycelium,  etc.,  already  in  the  plant? 
— a  number  of  infections  were  made  on  seedlings  germinated  and 
grown  antiseptically  in  tubes  as  follows  *  *  *  *  de^n 
picked  seeds  were  placed  singly,  by  means  of  forceps,  on  filter 
paper  at  the  bottom  of  Petri  dishes  properly  sterilized  by  heat. 
When  these  had  germinated  and  observation  showed  that  the 
whole  series  was  free  of  moulds  or  other  signs  of  contaminations, 
the  seedlings  were  removed  by  means  of  sterile  forceps,  and  trans- 
planted singly  into  sterilized  tubes  of  various  kinds  as  described 
below,  and  the  further  growth  allowed  to  proceed  in  the  light 
under  conditions  varied  as  will  be  seen  *  *  *  *  Preliminary 
experiments  soon  showed  that  the  Brome  seedlings  thus  raised 
from  seeds  treated  antiseptically  and  protected  from  the  first  by 
glass,  may  be  grown  for  weeks  and  even  for  a  couple  of  months 
in  such  tubes  under  proper  precautions,  and  I  set  myself  the  task 
of  ascertaining  how  such  cultures  would  behave  in  infection  exper- 
iments. *  *  *  *  This  experiment  is  interesting  not  only  as 
showing  that  plants  can  be  grown  and  infected  successfully  in 
these  closed  water-cultures,  but  especially  as  showing  the  contrast 
between  the  aerated  and  non-aeratecl  tubes,  for  since  the  infected 
seedlings  were  selected  in  each  case  from  the  same  Petri  dish 
cultures,  we  must  assume  that  the  difference  in  rate  of  develop- 
ment was  due  to  the  difference  of  ventilation,  and  perhaps  con- 
clude that  this  interferes  with  the  success  of  the  parasite,  as 
measured  by  the  somewhat  longer  inoculation  period.  It  is 
remarkable  how  dwarfed  the  continuously  aerated  plants  are, 
compared  with  those  in  the  closed  tubes,  owing  to  the  elongation 
of  the  leaves  of  the  latter.  It  is  clear,  therefore,  that  pure  cultures 
of  Uredo-spores  can  be  obtained  by  this  method,  and  it  is  equally 
clear  that  we  can  also  obtain  pure  cultures  of  the  host-plants, 
and  since  we  can  do  this,  there  is  no  reason  why  the  infection  of 
Uredineae  should  not  be  conducted  as  vigorously  and  exactly  as 
that  of  bacteria." 

Coons  (Ann.  Rep.  Agr.  Exp.  Sta.  Neb.  25:  222.)  in  1912  made 
inoculations  in   Petri   dishes   with   Gymnosporangium   Juniperi- 


(  HISTORICAL  477 

vnginianae  on  apple  leaves  to  determine  the  method  of  entrance 
of  the  germ  tubes.  Evidently  he  did  not  save  the  inoculations 
long  enough  to  observe  further  development.  We  make  the 
following  quotation  from  his  article:  "With  the  microscope  it 
was  possible  to  see  the  hyphae  from  the  sporidia  after  a  vagrant 
tortuous  growth  in  the  water,  bend  sharply  downward  at  the 
edge  of  the  drop  and  pass  into  the  cells  beneath.  This  last  obser- 
vation was  made"  with  leaves  washed  in  sterile  water  and  kept  in 
Petri  dishes.  These  were  inoculated  in  drops  of  water  and  marked 
by  circles  with  the  cork  borer." 

The  Petri  dish  method  of  infection  with  fungi  other  than  rusts 
has  been  tried  by  various  experimenters  as  shown  hj  the  two 
following  references.  Salmon  (Journ.  Bot.  41:  212.)  in  1903 
described  his  methods  with  the  powdery  mildews  in  these  words: 
"The  following  method  of  culture  for  infection  experiments  has 
been  adopted.  The  leaves  to  be  inoculated  are  cut  off  from  the 
plant  and  placed  on  wet  filter  paper  at  the  bottom  of  a  Petri  dish, 
the  under  surface  of  the  leaf  being  everywhere  pressed  into  contact 
with  the  wet  filter-paper.  If  the  experiment  is  to  be  continued  for 
more  than  a  week  or  ten  days,  a  seedling  with  the  first  leaf  attached 
to  the  seed  must  be  used.  The  Petri  dishes  can  be  placed  in  circu- 
lar dishes  of  about  the  same  depth  and  of  a  half-inch  greater 
diameter  and  the  intervening  space  at  the  sides  stuffed  with 
cotton-wool.  This  will  remove  all  danger  of  infection  from  foreign 
spores  after  the  experiment  has  been  set  up." 

In  1916  very  similar  methods  were  used  by  Blackmail  and 
Welsford  (Ann.  Bot.  30:  390.)  in  infection  work  with  Botrytis 
cinerea  described  as  follows:  "Before  infection  the  leaves  are 
washed  with  a  gentle  stream  of  sterile  distilled  water  to  remove  as 
far  as  possible  extraneous  spores  and  dust.  They  are  then  placed 
on  clamp  filter-paper  on  a  sterile  Petri  dish,  and  drops  of  the 
prepared  solution  containing  spores  placed  on  their  upper  surfaces." 

The  writers  were  not  aware  of  the  methods  of  the  preceding 
investigators  when  their  work  was  first  undertaken.  The  results 
we  obtained,  however,  with  Cronartium  ribicola  were  such  as  to 
justify  us  in  extending  the  experiments  to  various  other  rusts. 
These  experiments  have  now  been  carried  on  over  seven  seasons. 
The  number  of  hosts  thus  infected  with  various  species  has  ex- 
ceeded our  expectations.  The  improvement  of  our  methods 
through  experience  enabled  us  to  keep  leaves  alive  much  longer 
than  at  first  and  thereby  successful  inoculation  was  increased. 
It  is  deemed  advisable  to  make  a  more  detailed  record  here  of  our 
methods,  with  the  results  obtained,  in  order  that  they  may  be 
used  by  others,  since  our  experience  has  shown  decided  advantages 
with  this  method  especially  with  rusts  which  inhabit  the  less 
succulent  and  ephemeral  leaves. 


478  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   260. 


METHODS. 

Petri  dish  versus  pot  method.  Soon  after  finding  that  successful 
inoculation  of  Rihes  nigrum  could  be  made  in  Petri  dishes  with 
blister  rust,  it  was  decided  to  carry  on  a  series  of  tests  with  different 
species  of  Rihes  in  Petri  dishes  as  well  as  in  pots.  Tests  were  made 
with  both  I  and  II  stages.  In  Table  I  is  given  a  summary  of  all 
our  experiments  with  these  stages  in  Petri  dishes  and  pots,  regard- 
less of  whether  they  were  made  under  sunilar  conditions  or  not. 
This  shows  that  with  the  I  stage  out  of  one  hundred  and  seventy 
tests  made  in  Petri  dishes  66%  were  successful  and  according  to 
our  grade  of  marking  these  were  rated  poor  (+),  while  of  the  one 
hundred  and  twenty-three  tests  made  in  pots  78%  were  successful 
with  an  average  of  fair  ( — ) .  These  tests  favor  somewhat  the  pot 
method,  especially  as  regards  percentage  of  infection.  In  this  case 
it  is  to  be  remembered,  however,  that  many  more  leaves  were 
exposed  to  infection.  In  the  tests  with  the  II  stage,  where  the 
amount  of  uredospores  and  number  of  leaves  inoculated  were 
more  nearly  alike,  because  of  the  difficulty  of  obtaining  an  abun- 
dance of  the  spores,  the  results  wel-e  about  the  same.  In  this  case 
in  one  hundred  and  sixty-nine  tests  in  Petri  dishes  57%  were 
successful  with  an  average  rating  of  poor  (+),  while  of  the  fifty- 
six  tests  in  the  pots  57%  were  successful  with  an  average  rating 
of  fair  ( — ) . 

Several  comparative  tests  were  made  with  the  I  stage  on  leaves 
in  Petri  dishes  and  plants  in  pots,  with  the  other  conditions  as 
nearly  alike  as  possible,  on  twenty-four  species  and  varieties  of 
Rihes.  While  these  gave  somewhat  different  results  on  certain  of 
the  hosts,  sometimes  in  favor  of  the  Petri  dish  and  again  in  favor 
of  the  pot,  the  average  result  for  the  lot  was  about  the  same  from 
each  method,  favoring  slightly  the  pot.  We  concluded  at  the 
time,  taking  into  consideration  the  amount  of  inoculating  material 
and  the  number  of  leaves  used,  that  one  method  was  as  successful 
as  the  other.  We  were  not  able  to  make  similar  comparisons  with 
other  rusts  but  our  general  experience  with  those  inhabiting  leaves 
of  shrubs  and  trees  is  that  the  Petri  dish  method  has  certain 
advantages. 

Technique.  Where  a  considerable  number  of  inoculations  is  to 
be  made,  Petri  dishes  of  about  100  mm.  in  diameter  and  15  mm. 
deep  are  a  convenient  size  to  use.  A  larger  size  is  even  more 
desirable,  especially  when  few  are  required.  Our  usual  method 
has  been  to  stretch  two  well-washed  rubber  bands  loosely  across 
the  bottom  of  the  sterilized  dish,  and  on  these  is  placed  the  wet 
leaf  or  leaves.  When  the  cover  is  inserted  the  leaves  should  be 
near  the  top  but  not  touching  it.  Our  most  recent  method  has 
been  to  file  four  opposite  or  equally  distant  notches,  about  a 
quarter  of  an  inch  deep,  in  the  edge  of  the  bottom  dish  and  stretch 
the  rubber  bands  across  and  diagonally  through  these  to  hold  the 


METHODS  479 

leaves  out  of  the  water  below  but  free  from  pressure  above.  (See 
Plate  XXVIa.)  Glass  rods  with  a  flat  surface  below  can  be  used  in 
place  of  the  rubber  bands.  These,  however,  should  be  of  sufficient 
height  to  elevate  the  leaf  above  the  water  and  near  to  the  cover. 
A  small  amount  of  water  is  poured  in  the  bottom  of  the  dish.  The 
spores  are  dusted  or  brushed  off  the  inoculating  material  over  the 
exposed  surface  of  the  leaf.  In  case  the  I  and  II  stages  are  used 
it  is  better  to  place  the  lower  surface  of  the  leaf  uppermost,  since 
infection  usually  takes  place  through  the  stomates  which  are  more 
abundant  on  that  surface;  also  the  sori  that  result  in  such  cases 
usually  break  out  on  the  lower  surface  and  consequently  can  be 
watched  carefully  without  disturbing  the  leaf  or  removing  the 
cover.  In  case  the  inoculation  is  with  the  III  stage,  where  infec- 
tion generally  takes  place  by  direct  penetration  of  the  epidermis, 
it  is  better  to  place  the  upper  surface  of  the  leaf  uppermost,  as 
this  is  freer  from  hairs  which  hinder  infection.  Furthermore  the 
pycnial  stage  is  more  likely  to  appear  on  this  surface  and  it  is 
difficult  to  carry  the  infection  beyond  this  stage  because  of  the 
length  of  time  required.  The  Petri  dish  should  be  placed  where 
it  receives  direct  light  favorable  for  plant  growth.  North  light  or 
direct  sunlight  partially  screened  by  thin  white  paper  or  a  coating 
on  the  windows  is  desirable.  The  conditions  upon  which  infection 
is  successful  depend  largely  upon  the  following  factors — leaves, 
moisture,  light  and  heat. 

Leaves.  The  leaves  must  remain  in  fairly  healthy  condition 
from  seven  to  ten  days  and  in  some  cases  more  than  two  weeks 
after  inoculation.  Leaves  of  different  plants  vary  greatly  in  this 
respect.  As  a  rule  the  hardier  leaves  of  shrubs  and  trees  do  not 
succumb  as  quickly  as  those  of  herbaceous  plants.  Again  with 
some  plants,  as  the  grasses,  it  is  often  impossible  to  place  the 
whole  leaf  in  the  Petri  dish  because  of  its  size  and  mutilation  is 
more  or  less  harmful.  Enzymatic  or  other  changes  in  certain 
leaves  frequently  kill  them  before  infection  is  apparent,  but  the 
chief  difficulty  seems  to  be  with  molds  that  cause  decay.  This 
last  injury  can  be  reduced  or  delayed  by  very  thorough  washing 
of  both  sides  of  the  leaves  in  running  tap  water.  The  wet  leaf  is 
then  placed  in  the  Petri  dish.  Partial  sterilization  did  not  give 
so  effective  results  as  the  washing  in  water  alone.  This  is  a  matter, 
however,  that  may  need  further  investigation.  It  is  taken  for 
granted  that  in  the  selection  of  leaves  only  those  in  the  best  condi- 
tion, and,  where  possible,  of  a  size  smaller  than  the  Petri  dish 
will  be  selected;   also  that  they  are  free  from  natural  infection. 

Moisture.  The  moisture  in  the  bottom  of  the  Petri  dish  is 
sufficient  to  keep  the  air  fairly  well  saturated.  Considerable 
moisture  becomes  condensed  on  the  cover  in  close  proximity  to 
the  inoculated  surface  of  the  leaf,  thereby  making  conditions  for 
spore  germination  very  favorable.  It  is  necessary  from  time  to 
time  to  renew  the  water  in  the  bottom  of  the  dish  as  it  is  lost  by 


480  CONNECTICUT   EXPERIMENT   STATION  BULLETIN   260. 

evaporation.  This  may  be  added  by  pouring  it  in  the  dish  or  by 
spraying  it  over  the  leaves,  as  conditions  warrant.  The  dish 
should  never  be  allowed  to  become  entirely  dry  as  the  leaves  will 
wither  and  die  in  a  very  short  time.  On  the  other  hand  the 
amount  of  water  should  not  be  sufficient  to  touch  the  leaf  blade 
in  the  handling  that  is  necessary.  In  our  work  different  methods 
were  tried,  such  as  a  small  film  or  an  abundance  of  water  with 
the  leaf  directly  on  it.  The  method  described,  however,  seemed 
to  possess  the  most  merits  in  securing  abundance  of  infection  and 
freedom  from  molds. 

Light.  In  the  first  experiments  the  Petri  dishes  were  left  in  the 
diffused  light  of  the  culture  room  some  distance  from  the  window. 
Trouble  with  molds  suggested  that  better  results  might  be  ob- 
tained with  direct  light.  Comparative  tests  were  then  made  both 
with  inoculated  and  uninoculated  leaves  left  in  the  culture  room 
and  others  placed  in  the  small  laboratory  greenhouse  having  an 
eastern  exposure  but  with  the  light  cut  off  from  the  south  and 
west.  To  lessen  the  strong  sunlight  of  summer  the  glass  was 
shaded  by  paper.  These  tests  were  in  favor  of  the  direct  light  so 
that  practically  all  of  our  infections  have  been  made  in  this  green- 
house. Our  opinion  is  that  the  latter  place  is  more  favorable  for 
the  following  reasons.  First,  the  direct  light  on  the  leaves  seems 
to  keep  them  in  healthier  condition  so  that  molds  are  not  so 
troublesome  as  in  subdued  light.  Second,  this  action  on  the 
chloroplasts  favors  the  normal  photosynthetic  processes  which 
furnish  food  for  the  leaf  and  thereby  favor  the  more  vigorous 
development  of  the  fuiigus.  If  it  were  not  for  the  ease  of  examina- 
tion, etc.,  it  would  probably  be  better  in  all  cases  to  expose  the 
upper  surface  of  the  leaf  to  the  light  thereby  securing  full  benefit 
from  it  as  in  nature. 

It  is  surprising  how  long  some  leaves  remain  healthy  under  these 
optimum  conditions.  Not  infrequently  we  have  kept  leaves  green 
and  alive  for  three  or  four  weeks.  In  exceptional  cases  where  a 
callus  has  formed  at  the  base  of  the  petiole,  they  have  remained 
alive  even  longer.  In  one  case  a  Ruhus  leaf,  where  a  callus  had 
formed  and  rootlets  developed,  remained  ahve  for  a  couple  of 
months.  Plate  XXVIb  shows  a  black  currant  leaf  about  a  month 
after  it  was  placed  in  a  Petri  dish  developing  a  secondary  callus  at 
one  side  of  the  primary  one.  This  leaf  was  just  beginning  to  die 
when  photographed.  Plate  XXVId  shows  one  of  several  leaves  of 
Solidago  rugosa  that  remained  alive  and  green  three  months  in  the 
Petri  dishes  developing  from  the  calluses  formed  at  their  bases 
branched  rootlets  one  to  two  times  the  length  of  the  leaves.  These 
leaves  were  then  placed  in  sand  and  later  earth  added  in  the  hope 
that  they  might  develop  buds  and  new  plants  and  were  still  healthy 
and  green  after  four  months.  Either  the  addition  of  the  earth  or 
accidental  drying  out  caused  their  death  soon  afterward.  How- 
ever, one  had  formed  a  minute  plantlet  on  a  root  or  runner  de- 


GENERAL   RESULTS  481 

veloped  from  the  callus.  These  examples  are,  of  course,  excep- 
tional but  in  case  a  callus  develops  longer  life  is  assured.  Whether 
coating  the  end  of  the  petiole  with  melted  paraffin  would  favor 
callus  formation  has  not  been  determined. 

Heat.  It  has  been  shown  with  the  rusts,  as  with  other  fungi, 
that  spores  germinate  best  at  certain  temperatures  known  as  their 
optimum  and  that  maximum  temperatures  also  exist  beyond 
which  germination  ceases  to  take  place.  Doran  (Phytopath.  9: 
391-402.  S.  1919.)  worked  with  several  of  the  rusts  along  this 
line  and  he  found  that  for  the  aeciospores  of  Cronartium  rihicola 
the  optimum  temperature  was  12°C  and  the  maximum  19°C  and 
the  uredospores  had  an  optimum  temperature  of  two  degrees  and 
a  maximum  of  six  degrees  higher  than  those  of  the  aeciospores. 
In  our  experiments  the  ordinary  room  temperature  of  the  green- 
house in  spring  and  fall  seemed  favorable.  In  mid-summer, 
however,  the  temperature  reached  such  a  height  that  practically 
all  the  cultures  died  out.  To  obviate  this  difficulty  a  modification 
of  Hunt's  (Phytopath.  9:  211-12.  My.  1919.)  iceless  refrigerator 
was  used.  This  on  the  whole  kept  the  temperature  down  on  an 
average  only  a  few  degrees,  but  it  was  sufficient  to  favor  the 
cultures  over  those  outside.  However,  the  cloth  cut  down  the 
light  so  that  this  was  not  so  favorable.  A  cold  incubator  with  glass 
sides  which  can  be  kept  in  the  sunlight  at  a  desired  temperature 
would  be  a  very  valuable  adjunct  for  summer  inoculations. 

GENERAL   RESULTS. 

Advantages  and  disadvantages  of  method.  We  will  first  mention 
the  one  disadvantage  of  the  Petri  dish  method,  the  early  death  of 
the  leaves.  This  happens  more  quickly  with  some  leaves  than 
with  others  as  has  already  been  mentioned.  With  Cronartium 
rihicola  on  Rihes  it  was  only  an  occasional  disadvantage  as  most 
of  the  leaves  lived  long  enough  to  produce  mature  sori  of  uredinial 
and  occasionally  of  telial  stages.  With  such  tender  leaves  as 
clovers,  however,  death  of  the  leaves  often  occurred  too  early  to 
secure  definite  results.  With  Pyrus  the  leaves  usually  lived  long 
enough  to  secure  pycnia  but  not  long  enough  to  produce  aecia. 
A  combination  of  this  method  with  Ward's,  using  the  latter  for 
grasses  and  quick  growing  seedlings,  will  probably  solve  the 
problem  for  infection  of  most  hosts.  No  doubt  some  may  be 
disappointed  with  their  first  results  of  the  Petri  dish  method,  as 
experience  is  an  important  factor  in  obtaining  success. . 

The  advantages  must  be  evident  to  anyone  who  stops  to  con- 
sider the  matter.  First,  we  mention  compactness.  Petri  dishes 
occupy  little  space  and  by  means  of  glass  or  wire  shelves  many 
can  be  used  in  a  small  area.  Ordinarily  we  have  used  them  on 
glass  shelves  in  the  iceless  refrigerator  or  on  a  cement  greenhouse 
bench  containing  sand  which  has  been  covered  with  botanical 
driers  soaked  in  corrosive  sublimate  to  prevent  molding.     The 


482  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   260. 

second  advantage  is  economy  of  material.  Often  one  plant  will 
furnish  enough  leaves  for  many  experiments  whereas  if  the  pot 
method  is  used  the  whole  plant  is  involved.  A  third  advantage  is 
ease  and  exactness  of  observation.  With  a  leafy  plant  of  some 
size  the  first  appearance  of  the  sori  may  escape  observation. 
These  can  be  observed  through  the  Petri  dish  cover  very  easily 
and  quickly.  By  this  method  we  have  found  uredinial  sori  within 
six  days  and  twenty- two  hours  after  inoculation.  This  is  earlier 
than  we  have  ever  found  them  on  plants  in  pots.  A  fourth  advan- 
tage is  the  surety  of  pure  cultures  since  there  is  little  danger,  com- 
pared with  plants  in  pots,  of  spores  of  other  rusts  reaching  the 
inoculated  leaves.  Better  control  of  moisture  for  securing  germi- 
nation of  spores  is  another  advantage. 

Rusts  used  in  the  experiments.  Altogether  thirteen  different 
genera  of  rusts  were  experimented  with,  as  follows:  Caeoma, 
Coleosporium,  Cronartium,  Gymnoconia,  Gymnosporangium,  Kuehn- 
eola,  Melampsora,  Melampsoridium,  Melampsoropsis,  Phragmid- 
ium,  Puccinia,  Pucciniastrum  and  Uromyces.  We  were  successful 
in  producing  one  or  more  infections  with  all  of  these  excepting  the 
first.  Under  these  genera  forty-five  different  species  were  used 
and  successful  inoculations  were  secured  with  all  but  seventeen. 
Many  different  hosts  were  inoculated  with  these.  Some  of  these 
failures  were  due  to  the  use  of  the  wrong  host.  In  other  cases 
failure  was  due  to  poor  inoculating  material.  It  is  quite  probable 
that  in  some  tests  the  leaves  died  before  the  sori  had  time  to 
develop.  The  most  extended  experiments  were  with  Cronartium 
ribicola  involving  three  hundred  and  thirty-nine  tests  on  thirty- 
eight  different  species  and  varieties.  Tests  were  made  with  all 
spore  stages,  O,  I,  II  and  III.  No  results  were  obtained  with  the 
O  stage,  as  was  to  be  expected.  Most  inoculations  were  made 
with  the  I  and  II  stages.  No  new  relationships  between  supposedly 
distinct  species  were  found.  Several  new  hosts,  however,  were 
secured  through  inoculations  and  a  few  old  hosts  are  reported  for 
the  first  time  experimentally. 

In  interpreting  the  results  of  the  inoculations  we  have  used  the 
following  terms:  failed,  poor,  fair,  good  and  excellent.  These, 
except  the  first,  have  been  used  in  a  general  rather  than  in  an 
exact  sense.  Usually  the  number  of  sori  occurring  has  indicated 
the  class.  With  the  pot  experiments,  however,  the  number  of 
infected  leaves  as  well  as  the  number  of  sori  was  taken  into  con- 
sideration. The  amount  of  inoculating  material  used,  especially 
the  II  stage,  was  also  a  factor  in  grading.  As  a  rule  poor  indicates 
that  fewer  than  five  sori  developed.  Excellent  implies  the  develop- 
ment of  forty  or  more  on  a  leaf  or  leaves  in  a  Petri  dish  and  an 
even  greater  total  number  on  the  leaves  of  a  plant  in  a  pot.  Good 
and  fair  are  intermediate  terms.  The  inoculation  number  and 
date,  as  well  as  source  of  inoculating  material  and  host  inoculated, 
are  given  with  each  experiment.  The  details  of  the  experiments 
both  successful  and  unsuccessful  are  given  in  the  following  pages. 


DETAILS    OF   INOCULATIONS   AND    INFECTIONS  483 


DETAILS    OF   INOCULATIONS   AND   INFECTIONS. 

Caeor^a  nitens  Schw. 

None  of  the  inoculations  made  with  this  short  cycled  form  was 
successful.  Comparison  should  be  made  with  similar  successful 
inoculations  with  the  long  cycled  form  given  here  under  Gymno- 
conia  inter stitialis.  We  thought  at  one  time  that  possibly  this 
short  cycled  form  was  the  Caeoma  stage  of  some  other  rust,  most 
likely  Melampsora,  but  our  failures  to  inoculate  the  various  species 
of  Populus,  Salix  and  Betula  discredit  this  supposition.  Likewise 
the  failure  to  inoculate  mature  leaves  of  Ruhus  species  has  led  us 
finally  to  believe  that  infection  takes  place  with  this  short  cycled 
form  only  through  the  young  tissues  especially  the  underground 
shoots.     See  articles  in  Bull.  222,  p.  469,  of  this  Station. 

0  stage  from  Ruhus  villosus  ( R.  canadensis) :  on  R.  villosus,  894  (upper 
surface),  895  (lower  surface),  896  (cut  Surface),  My.  27,  '19,  failed. 

1  stage  from  Ruhus  allegheniensis  (R.  villosus):  on  R.  allegheniensis, 
1349  (wild),  1353  (Erie),  1355  (Snyder),  Je.  22,  '20,  failed:  on  R.  villosus, 
1347,  Je.  22,  '20,  failed:    on  R.  occidentalis,  1345,  1351,  Je.  22,  '20,  failed. 

I  stage  from  Ruhus  villosus:  on  Betula  lenta,  904,  91 1,  918,  My.  27,  '19, 
failed:  on  B.  populifolia,  903,  910,  917,  My.  27,  '19,  failed:  on  Populus 
deltoides,  907,  914,  921,  My.  27,  '19,  failed:  on  P.  grandidentata,  901,  908, 
915,  My.  27,  '19,  failed:  on  P.  tremuloides,  902,  909,  916,  My.  27,  '19, 
failed:  on  Populus  sp.,  363,  Je.  22,  '18,  failed:  on  Ruhus  hispidus,  4336, 
Je.  15,  '23,  failed';  4351,  Je.  20,  '23,  failed:  on  R.  villosus,  332,  333,  334, 
335,  Je.  6,  '18,  failed;  958,  Je.  11,  '19,  failed;  4004,  Je.  15,  '22,  failed; 
4289,  4292,  Je.  1,  '23,  failed;  4327,  Je.  12,  '23,  failed;  4337,  Je.  15,  '23, 
failed;  4344,  Je.  16,  '23,  failed;  4349,  Je.  20,  '23,  failed;  4579,  4582,  Jl. 
2,  '24,  failed:  on  Ruhus  sp.  (cult,  blackberry),  4007,  Je.  15,  '22,  failed; 
4288,  4291,  Je.  1,  '23,  failed;  4328,  Je.  12,  '23,  failed;  4350,  Je.  20,  '23, 
failed;  on  Ruhus  sps.,  (wild  and  cult,  raspberry),  4005,  4006,  Je.  15,  '22, 
failed;  4290,  4293,  Je.  1,  '23,  failed:  on  Salix  sps.,  905,  906,  912,  913, 
919,  920,  My.  27,  '19,  failed. 

Coleosporium  delicatulum  (Arth.  &  Kern)  Hedge.  &  Long. 

The  successful  inoculation,  on  Solidago  graminifolia  Nuttallii, 
was  with  the  host  on  which  the  II  and  III  stages  of  this  rust  most 
commonly  occur  in  this  state.  The  senior  writer  in  years  previous 
had  also  inoculated  the  same  host  in  crock  experiments.  One  out 
of  four  inoculations  was  successful  as  follows: 

I  stage  from  Pinus  rigida:  on  Aster  sps.,  807,  808,  My.  19,  '19,  failed: 
on  Solidago  graminifolia  Nuttallii,  814,  My.  20,  '19,  fair,  II:  on  S.  rugosa, 
806,  My.  19,  '19,  failed. 

Coleosporium  Solidaginis  (Schw.)  Thuem. 

Inoculations  of  the  I  stage  from  Pinus  rigida  were  successful  on 
Solidago  rugosa,  S.  sempervirens ,  and  of  the  II  stage  from  Solidago 
sp.  on  Solidago  sp.  and  S.  rugosa.  Five  out  of  twelve  inoculations, 
or  42%,  were  successful  as  follows: 


484  CONNECTICUT    EXPERIMENT   STATION  BULLETIN   260. 

I  stage  from  Pinus  rigida:  on  Solidago  rugosa,  933,  Je.  4,  '19,  good,  II; 
1344,  Je.  17,  '20,  excellent,  II;  4568,  Je.  11,  '24,  poor,  II:  on  Solidago 
semper vir ens,  893,  My.  26,  '19,  poor,  II. 

II  stage  from  Solidago  rugosa:  on  Aster  laevis,  579,  O.  5,  '18,  failed:  on 
Solidago  rugosa,  578,    O.  5,  '18,  failed;    11.15,  O.  27,  '19,  failed. 

II  stage  from  Solidago  sp. :  on  Aster  laevis,  1021,  Jl.  19,  '19,  failed:  on 
Aster  sp.,  1522,  O.  28,  '20,  failed:  on  Solidago  graminifolia  Nuttallii,  1019, 
Jl.  19,  '19,  failed:  on  S.  rugosa,  1020,  Jl.  19,  '19,  failed;  1521,  O.  28,  '20, 
poor,  II:    on  Solidago  sp.,  1022,  Jl.  19,  '19,  fair,  II. 

Cronartium  Comptoniae  Arth. 

Successful  inoculations  on  Myrica  asplenifolia  were  made  with 
the  I  stage  from  the  five  species  of  Pinus  tried.  The  inocula- 
tions with  the  III  stage  on  the  pines  probably  failed,  at  least 
nothing  definite  showed  to  the  naked  eye.  Our  inoculations  of 
plants  in  crocks,  however,  showed  that  there  is  very  little  visible 
sign  of  successful  inoculation.  At  one  time  the  Cronartiums  were 
classed  together  under  C.  asdepiadeum  but  our  unsuccessful 
attempts  to  inoculate  Rihes  and  Quercus  add  weight  to  the  behef 
that  the  rusts  on  these  two  hosts  and  Myrica  are  cUstinct  species 
as  now  regarded.    The  details  Of  the  inoculations  follow: 

I  stage  from  Pinus  austriaca:  on  Myrica  (Comptonia)  asplenifolia, 
4556,  My.  28,  '24,  excellent,  II. 

I  stage  from  Pinus  montana  Mugho:  on  Myrica  asplenifolia,  4285, 
My.  31,  '23,  excellent,  II;  4566,  Je.  10,  '24,  excellent,  II.  See  Plate  XXVIa. 

I  stage  from  Pinus  ponderosa:  on  Myrica  asplenifolia,  4286,  My.  31, 
'23,  excellent,  II. 

I  stage  from  Pinus  rigida:  on  Myrica  asplenifolia,  342,  Je.  6,  '18,  good, 
II:     on  Rihes  nigrum,  899,  My.  27,  '19,  failed. 

I  stage  from  Pinus  sylvestris:  on' Myrica  asplenifolia,  340,  Je.  6,  '18, 
good,  II:  on  Rihes  nigrum,  302,  My.  27,  '18,  failed:  on  R.  vulgare,  301, 
My.  27,  '18,  failed:    on  Quercus  alba,  341,  Je.  6.,  '18,  failed. 

III  stage  from  Myrica  asplenifolia:  on  Pinus  austriaca,  1079,  S.  15,  '19, 
(?)  failed:    on  P.  sylvestris,  1078,  S.  15,  '19,  (?)  failed. 

Cronartium  occidentale  Hedge,  Beth.  &  Hunt. 

The  inoculations  with  the  I  stage  from  Pinus  monophylla  were 
all  made  on  May  28,  1920  and  were  successful  on  the  following 
hosts:  Ribes  americanum,  R.  aurewn,  R.  aureum  chrysococcum, 
R.  Cynoshati,  R.  divaricatum,  R.  Grossularia  (uva-crispa) ,  R.  hir- 
tellum,  R.  intermedium,  R.  nigrum,  R.  nigrum  aconitifolium,  R. 
odoratum,  R.  oxyacanthoides,  R.  robustum,  and  Rihes  sps.  (cult, 
gooseberries).  Several  were  apparently  new  hosts  for  this  rust. 
The  inoculations  were  in  triplicate,  the  average  results  being  given. 
We  are  indebted  to  Bethel  and  others  of  the  U.  S.  Department  of 
Agriculture  for  the  inoculating  material  used. 

I  stage  from  Pinus  monophylla:  on  Rihes  alpestre,  1270,  failed:  on  R, 
alpinumd^,  1285,  failed:  on  R.  americanum,  1273,  poor,  II,  III:  on  R. 
aureum,  1267,  good,  II,  III:  on  R.  caucasicum,  1269,  failed:  on  R. 
aureum  chrysococcum,  1276,  excellent,  II:  on  R.  curvatum,  1271,  failed: 
on  R.  Cynoshati,  1275,  good,  II,  III:     on  R.  divaricatum,  1272,  fair,  II: 


DETAILS   OF   iNOCULATIONS   AND    INFECTIONS  485 

on  R.  Grossularia  (uva-crispa),  1289,  fair,  II,  III:  on  R.  giraldii,  1268, 
failed:  on  R.  hirtelhim,  1281,  fair,  II:  on  R.  holosericeum,  1284,  failed: 
on  R.  intermedium,  1278,  fair,  III:  on  R.  luridum,  1280,  failed:  on  R. 
nigrum,  1279,  poor,  II:  on  R.  nigrum  aconilifolium,  1287,  poor,  II:  on 
R.  odoratum,  1290,  good,  II:  on  R.  oxyacanthoides,  1291,  good,  II,  III: 
on  R.  robustuni,  1277,  poor,  II:  on  R.  stenocarpum,  1288,  failed:  on  R. 
vulgare  (Fay's  Prolific),  1274,  failed;  1283  (small  currant),  failed;  1282, 
(white  currant),  failed:  Ribes  sps.  (large  cult,  gooseberry),  1286,  poor, 
II;     1292  (Smith's  small  gooseberry),  poor,  II,  III. 

II  stage  from  Ribes  aureum  chrysococcum  (in  Petri  dish) :  on  Ribes 
aureum.  chrysococcum,  1276  (2),  Je.  17,  '20,  failed. 

II  stage  from  Ribes  gracillimimi:  on  R.  americanum,  4403,  Jl.  14,  '23, 
failed:  on  R.  aureum,  4404,  Jl.  14,  '23,  failed:  on  R.  nigrum,  4402,  Jl.  14, 
'23,  failed. 

Cronartiuni  ribicola  Fisch.  de  Waldh. 

Inoculations  with  I  stage  from  Pinus  Strobus.  In  the  experi- 
ments with  the  I  stage  thirty-eight  species  and  varieties  of  Ribes 
were  used  and  one  hundred  and  seventy- two  inoculations  made. 
Of  these  one  hundred  and  six,  or  62%,  were  successful,  despite 
using  old  spores  and  inoculating  the  upper  surface  in  a  number  of 
cases.  Ribes  nigrum,  with  twenty-seven  tests  of  which  nearly  78% 
produced  infection,  and  Ribes  oxyacanthoides,  with  eight  inocula- 
tions and  87%  of  infection,  gave  the  best  results.  The  following 
species  also  became  infected:  R.  alpinum9,  R.  americanum,  R. 
aureum,  R.  aureum  chrysococcum,  R.  caucasicum,  R.  Cynosbati,  R. 
Cynosbati  inerme,  R.  diacantha,  R.  divaricatum,  R.  fasciculatum 
chinense,  R.  Grossularia  (uva-crispa),  R.  hirtellum,  R.  holoseri- 
ceum, R.  intermedium,  R.  longiflorum,  R.  luridum,  R.nigruyn  aco- 
nitifolium,  R.  odoratum,  R.  robustum,  R.  vulgare,  R.  vulgare  (Faj^'s 
Prolific),  R.  vulgare  (Small  Currant),  R.  vulgare  (White  Currant), 
Ribes  sp.  (large  gooseberry)  and  Ribes  sp.  (Smith's  Small  goose- 
berry). We  are  indebted  to  the  Arnold  Arboretum  for  most  of 
the  species  of  Ribes  used  in  these  and  the  other  inoculations. 

Uniform  failure  to  infect  leaves  when  spores  were  placed  on  the 
upper  surface,  where  there  are  few  or  no  stomates,  proves  infection 
takes  place  only  through  these,  as  is  also  shown  by  actual  obser- 
vation. It  is  interesting,  also,  to  note  that  good  infection  took 
place  with  spores  35  days  old  and  poor  with  those  49  days  old 
(t.  e.,  that  long  after  the  branches  containing  the  aecial  spores  were 
cut  from  the  tree  and  left  in  the  laboratory.) 

I  stage  from  Pinus  Strobus:  on  Ribes  alpestre,  685,  Ap.  28,  '19,  failed; 
787,  My.  13,  '19,  failed;  1313,  My.  29,  '20,  failed:  on  R.  alpinum  9,  687, 
Ap.  28,  '19,  failed;  792,  My.  13,  '19,  poor,  II,  III:  on  R.  alpinum d",  312, 
Je.  4,  '18,  failed;  777,  My.  13,  '19,  failed;  886,  My.  22,  '19,  failed;  929, 
Je.  4,  '19,  failed;  1294,  My.  29,  '20,  failed:  on  R.  americanum,  304,  309, 
Je.  4,  '18,  poor,  II;  707,  Ap.  28,  '19,  fair,  II;  715,  Ap.  28,  '19,  good,  II; 
726,  My.  2,  '19,  failed  (upper  surface);  762,  My.  13,  '19,  failed;  783, 
My.  13,  '19,  fair,  II;  1315,  My.  29,  '20,  poor,  II;  1331,  Je.  3,  '20,  failed?: 
on  R.  aureum,  313,  Je.  4,  '18,  failed;  671,  Ap.  28,  '19,  failed;  725,  My.  2, 
'19,  failed  (upper  surface);  779,  My.  13,  '19,  failed;  1319,  My.  29,  '20, 
fair,  II:  on  R.  aureum  chrysococcum,  305,  Je.  4,  '18,  poor,  II;  778,  My.  13, 


486  CONNECTICUT   EXPERIMENT   STATION  BULLETIN   260. 

'19,  fair,  II;  888,  My.  22,  '19,  failed;  932,  Je.  4,  '19,  failed;  1305,  My.  29, 
'20,  fair,  II:  on  R.  caucasicum,  306,  Je.  4,  'IS,  fair,  II;  697,  Ap.  28,  '19, 
fair,  II;  782,  My.  13,  '19,  fair,  II;  1314,  My.  29,  '20,  poor,  II:  on  R. 
curvatum,  786,  My.  13,  '19,  failed;  885,  My.  22,  '19,  failed;  1301,  My.  29, 
'20,  failed:  on  R.  Cynosbati,  789,  My.  13,  '19,  fair,  II;  1317,  My.  29,  '20, 
good,  II:  on  R.  Cynosbati  inerme,  770,  My.  13,  '19,  fair,  II:  on  R.  dia~ 
cantha,  689,  Ap.  28,  '19,  fair,  II:  on  R.  divaricatum,  324,  Je.  4,  '18,  fair, 
II;  679,  Ap.  28,  '19,  good,  II;  727,  My.  2,  '19,  failed  (inoc.  on  upper 
surface);  758,  My.  13,  '19,  fair,  II;  1306,  My.  29,  '20,  fair,  II:  on  R. 
fasciculatum  chinense,  699,  Ap.  28,  '19,  fair,  II;  795,  My.  13,  '19,  poor,  II: 
on  R.  Grossularia,  303,  Je.  4,  '18,  failed;  693,  Ap.  28,  '19,  failed:  on  R. 
Grossularia  {uva-crispa),  772,  My.  13,  '19,  fair,  II;  1296,  My.  29,  '20, 
fair,  II:  on  R.  giraldii,  695,  Ap.  28,  '19,  failed;  729,  My.  2,  '19,  failed 
(inoc.  on  upper  surface);  785,  791,  My.  13,  '19,  failed;  887,  My.  22,  '19, 
failed;  1310,  My.  29,  '20,  failed:  on  R.  hirtellum,  327,  Je.  4,  '18,  poor,  II; 
701,  Ap.  28,  '19,  fair,  II;  730,  My.  2,  '19,  failed  (inoc.  on  upper  surface); 
1293,  My.  31,  '20,  fair,  II:  on  R.  holosericeum,  321,  Je.  4,  '18,  poor,  II; 
1318,  My.  29,  '20,  fair,  II:  on  R.  intermedium,  325,  Je.  4,  '18,  failed;  717, 
Ap.  28,  '19,  good,  II;  732,  My.  2,  '19,  failed  (inoc.  on  upper  surface);  760 
My.  13,  '19,  fair,  II;  1312,  My.  29,  '20,  fair,  II:  on  R.  longiflorum,  316, 
Je.  4,  '18,  poor,  II:  on  R.  luridum,  691,  Ap.  28,  '19,  good,  II;  731,  My.  2, 
'19,  failed  (inoc.  on  upper  surface) ;  756,  My.  13,  '19,  fair,  II;  784,  My.  13, 
'19,  failed;  1308,  My.  29,  '20,  fair,  II:  on  R.  multi flor um,  Zll,  3 e.  4:,'!% 
failed:  on  R.  nigrum,  298,  My.  21,  '18,  good,  II;  317,  Je.  4,  '18,  poor,  II; 
328,  Je.  3,  '18,  good,  II;  330,  Je.  5,  '18,  good,  II,  III;  345,  My.  23-4, 
'18,  good,  II;  350,  Je.  12,  '18,  failed  (spores  43  days  old);  351,  Je.  12,  '18, 
failed  (spores  39  days  old);  352,  Je.  12,  '18,  good,  II  (spores  35  days  old); 
365,  Je.  26,  '18,  poor,  II  (spores  49  days  old);  368,  Jl.  23,  '18,  failed  (spores 
76  days  old);  644,  N.  26,  '18,  poor,  II;  658,  Ap.  10,  '19,  good,  II;  661,  Ap. 
12,  '19,  fair,  II;  670,  Ap.  21.  ^19,  excellent,  II;  674  Ap.  28,  '19,  good,  11;  683, 
Ap.  28,  '19,  excellent,  II;  734,  My.  2,  '19,  failed,  (inoc.  on  upper  surface); 
741,  My.  2,  '19,  excellent  (inoc.  on  lower  surface);  781,  My.  13,  '19,  fair, 
II;  891,  My.  23,  '19,  failed  (spores  left  45  days  in  Petri  dish);  892,  My.  23, 
'19,  failed  (spores  45  days  old);  1304,  My.  29,  '20,  fair,  II;  4008,  Je.  15,  '22, 
fair,  II:  on  R.  nigrum  aconitifolium,  930,  Je.  4,  '19,  failed;  1302,  My.  29, 
'20,  fair,  II:  on  R.  odoratum,  1300,  My.  29,  '20,  good,  II:  on  R.  orientale, 
319,  Je.  4,  '18,  failed:  on  R.  oxyacanthoides,  326,  Je.  4,  '18,  good,  II; 
673,  719,  Ap.  28,  '19,  excellent,  II;  740,  My.  2,  '19,  failed  (inoc.  on  upper 
surface);  780,  My.  13,  '19,  /air,  II;  1299,  My.  29,  '20,  fair,  II:  on  R. 
pinetorum,  315,  Je.  4,  '18,  failed:  on  R.  robustum,  711,  Ap.  28,  '19,  poor, 
II;  775,  My.  13,  '19,  failed;  931,  Je.  4,  '19,  good,  II;  1316,  My.  29,  '20, 
fair,  II;  1332,  Je.  3,  '20,  failed?:  on  R.  stenocarpum,  314,  Je.  4,  '18,  failed; 
776,  My.  13,'19,  failed;  1298,  My.  29,  '20,  failed:  on  P.  tenue,  709,  Ap.  28,'19, 
failed;  737,  My.  2,  '19,  failed  (inoc.  on  upper  surface);  768,  My.  13,  '19, 
failed;  1295,  My.  29,  '20,  failed:  on  R.  urceolatum,  310,  Je.  4,  '18,  failed:  on 
R.  vulgare,  320,  Je.  4,  '18,  fair,  II;  677,  Ap.  28,  '19,  good,  II;_738,  My.  2,  '19, 
failed  (inoc.  on  upper  surface):  on  R.  vulgare  (Fay's  Prolific),  308,  Je.  4, 
'18,  fair,  II;  657,  Ap.  10,  '19,  fair,  II;  660,  Ap.  12,  '19,  fair,  II;  672,  Ap.  28, 
'19,  good,  II;  713,  Ap.  28,  '19,  poor,  II;  728,  My.  2,  '19,  failed  (inoc.  on 
upper  surface);  764,  My.  13,  '19,  good,  II;  1307,  My.  29,  '20,  poor,  II:  on 
R.  vulgare  (small  currant),  318,  Je.  4,  '18,  fair,  II;  705,  Ap.  28,  '19,  fair, 
II;  735,  My.  2,  '19,  poor  (1  sorus,  II;  prob.  accidental,  inoc.  on  upper 
surface);  1309,  My.  29,  '20,  poor,  II:  on  R.  vulgare  (white  currant),  307, 
Je.  4,  '18,  fair,  II;  721,  Ap.  28,  '19,  good,  II;  739,  My.  2,  '19,  failed  (inoc. 
on  upper  surface);  1311,  My.  29,  '20,  fair,  II:  on  Ribes  sp.  (large  goose- 
berry), 323,  Je.  4,  '18,  good,  II;  675,  Ap.  28,  '19,  poor,  II;  681,  Ap.  28,  '19, 
failed;  733,  My.  2,  '19,  failed  (inoc.  on  upper  surface);  774,  My.  13,  '19, 
failed;  1303,  My.  29,  '20,  failed:  on  Rihes  sp.  (Smith's  small  gooseberry), 
322,  Je.  4,  '18,  poor,  II;  703,  Ap.  28,  '19,  fair,  II;  736,  My.  2,  '19,  failed 
(inoc.  on  upper  surface);  766,  My.  13,  '19,  failed;  1297,  My.  29,  '20, 
failed.     See  Plate  XXVd. 


DETAILS    OF   INOCULATIONS   AND    INFECTIONS  487 

Inoculations  with  I  and  repeating  with  II  stage.  These  inocula- 
tions all  started  with  the  I  spores  from  Pinus  Strohus  on  the 
various  species  of  Ribes  and  then  were  repeated  on  the  same 
species  of  Ribes  through  the  11  spores  produced  in  the  successive 
generations.  In  this  way  we  were  able  to  produce  from  one  to 
nine  distinct  generations  on  the  different  hosts.  The  most  suc- 
cessful host  for  inoculation  was  Ribes  nigrum  on  which  in  the  best 
test  were  produced  one  generation  from  the  I  spores  and  eight 
generations  from  the  II  spores  before  failure  resulted  on  account 
of  the  very  warm  summer  weather.  In  this  series  the  III.  stage 
appeared  with  the  II  in  the  seventh  generation.  We  know  of  no 
one  who  has  carried  on  so  extended  a  generation  test  under  such 
exact  conditions.  Other  hosts  on  which  the  rust  was  carried  for 
five  or  more  generations  were  Ribes  Cynosbati  and  R.  vulgar e. 

1,  II  stages  on  Ribes  alpinum  9  •'  I  stage  on  792  (1),  My.  13,  '19,  poor, 
II,  III;   II  on  792  (2),  Je.  5,  good,  II,  III. 

I,  II  stages  on  R.  americanum:  I  stage  on  707  (1),  Ap.  28,  '19,  good, 
II;  II  on  707  (2),  My.  12,  failed.  I  on  715  (1),  Ap.  28,  '19,  fair,  II;  II  on 
715  (2),  My.  12,  poor,  II;    II  on  715  (3),  Je.  5,  failed. 

I,  II  stages  on  R.  Cynosbati:  I  stage  on  789  (1),  My.  13,  '19,  fair,  II; 
II  on  789  (2),  Je.  5,  poor,  II;  II  on  789  (3),  Je.  23,  poor,  II;  II  on  789  (4), 
Jl.  15,  poor,  II;  II  on  789  (5),  Jl.  25  and  Au.  5,  poor,  II;  II  on  789  (6), 
Au.  13,  failed. 

I,  II  stages  on  R.fasciculatum  chinense:  I  stage  on  699  (1),  Ap.  28,  '19, 
fair,  II;   II  on  699  (2),  My.  12,  poor,  II;   II  on  699  (3),  Je.  5,  poor,  II. 

I,  II  stages  on  R.  hirtellum:  I  on  701  (1),  Ap.  28,  '19,  fair,  II;  II  on  701 
(2),  My.  12,  failed. 

I,  II  stages  on  R.  intermedium:  I  stage  on  717  (1)  ,Ap.  28,  '19,  fair,  II; 
II  on  717  (2),  My.  14,  poor,  II;   II  on  717  (3),  Je.  5,  failed. 

I,  II  stages  on  R.  luridum:  I  stage  on  691  (1),  Ap.  28,  '19,  good,  II; 
II  on  691  (2),  My.  12,  poor,  II;   II  on  691  (3),  Je.  5,  fair,  II. 

I,  II  stages  on  R.  nigrum:  I  stage  on  658  (1),  Ap.  10,  '19,  good,  II;  II 
on  658  (2),  Ap.  25  and  My.  3,  fair,  II;  II  on  568  (3),  My.  9  and  12,  poor, 
II;  II  on  568  (4),  Je.  4  and  23,  failed.  I  stage  on  661  (1),  Ap.  12,  '19, 
good,  II;  II  on  661  (2),  Ap.  25  and  My.  3,  good,  II;  II  on  661  (3),  My. 
12-13,  good,  II;  II  on  661  (4),  My.  24  and  28,  good,  II;  II  on  661  (5), 
Je.  10  and  16,  good,  II;  II  on  661  (6),  Je.  20  and  23,  fair,  II;  II  on  661  (7), 
Jl.  14,  18  and  25,  poor,  II  and  III;  II  on  661  (8),  Jl.  25,  28  and  Au.  5, 
poor,  II;  II  on  661  (9),  Au.  13  and  26,  fair,  II,  III;  II  on  661  (10),  Au.  26, 
failed.  I  stage  on  670  (1),  Ap.  21,  '19,  excellent,  II;  II  on  670  (2),  My.  1, 
excellent,  II;  II  on  670  (3),  My.  12,  good,  II;  II  on  670  (4),  My.  28,  good, 
II;  II  on  670  (5),  Je.  10,  16,  good,  II;  II  on  670  (6),  Je.  20  and  23,  fair, 
II;  II  on  670  (7),  Jl.  23,  28,  Au.  4,  poor,  II;  II  on  670  (8),  Au.  26,.  poor, 
II.  I  stage  on  674  (1),  Ap.  28,  '19,  good,  II;  II  on  674  (2),  My.  12,  fair, 
II;  II  on  674  (3),  Je.  5,  failed.  I  stage  on  997  (1),  Je.  16,  '19,  excellent, 
II;  II  on  997  (2),  JL  12,  fair,  II,  III;  II  on  997  (3),  Jl.  24,  28,  30,  fair,  II; 
II  on  997  (4),  Au.  5  and  13,  poor,  II. 

I,  II  stages  on  R.  oxyacanthoides:  I  stage  on  673  (1),  Ap.  28,  '19,  excel- 
lent, II;  II  on  673  (2),  My.  12,  failed.  I  stage  on  719  (1),  Ap.  28,  '19, 
excellent,  II;  II  on  719  (2),  My.  12,  good,  II;  II  on  719  (3),  Je.  5  and  23, 
failed. 

I,  II  stages  on  R.  robustum:  I  stage  on  931  (1),  Je.  4,  '19,  good,  II;  II 
on  931  (2),  Je.  23,  poor,  II;  II  on  931  (3),  Jl.  15,  18  and  21,  poor,  II;  II 
on  931  (4),  Au.  1,  failed. 

I,  II  stages  on  R.  vulgare:  I  stage  on  657  (1),  Ap.  10,  '19,  fair,  II;  II 
on  657  (2),  Ap.  23,  My.  3,  poor,  II;  II  on  657  (3),  My.  9  and  13,  poor,  II; 


488  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   260. 

II  on  657  (4),  My.  22,  poor,  II;  II  on  657  (5),  Je.  5,  poor,  II;  II  on  657 
(6),  Jl.  15,  failed.  I  stage  on  660  (1),  Ap.  12,  '19,  fair,  II;  II  on  660  (2), 
Ap.  25,  My.  3,  fair,  II;  II  on  660  (3),  My.  9  and  13,  poor,  II;  II  on  660 
(4),  My.  21,  failed. 

I,  II  stages  on  R.  vulgare  (Fay's  Prolific):  I  on  672  (1),  Ap.  28,  '19, 
good,  II;  II  on  672  (2),  My.  12,  failed. 

I,  II  stages  on  R.  vulgare  (small  currant):  I  stage  on  705  (1),  Ap.  28, 
'19,  fair,  II;    II  on  705  (2),  My.  12,  poor,  II;    II  on  705  (3),  Je.  5,  failed. 

I,  II  stages  on  R.  vulgare  (white  currant):  I  stage  on  721  (1),  Ap.  28, 
'19,  good,  II;    II  on  721  (2),  My.  12,  failed. 

I,  II  stages  on  Ribes  sp.  (large  gooseberry):  I  stage  on  675  (1),  Ap.  28, 
'19,  poor,  II;    II  on  675  (2),  My.  12,  failed. 

Inoculations  with  II  stage  from  Rihes  nigrum.  In  this  series  the 
II  spores  were  all  from  Ribes  riigrum  and  were  successful  on  the 
following  hosts:  Ribes  alpinum^,  R-  americanum,  R.  aureum 
chrysocoGcuni;  R.  Cynoshati,  R.  Cynoshati  inerme,  R.  divaricatuin, 
R.  fasciculatum  chinense,  R.  Grossularia  (uva-crispa) ,  R.  hirtellum, 
R.  holosericeum,  R.  intermedium,  R.  longiflorum,  R.  luridum,  R. 
nigrum,  R.  nigrum  aconiti folium,  R.  oxyacanthoides,  R.  rohustum, 
R.  tenue,  R.  vulgare,  Rihes  sp.  (Smith's  small  gooseberry).  That 
twenty  species  took  out  of  thirty-one  tried,  as  compared  with 
fifteen  out  of  twenty-five  where  the  II  spores  were  from  Rihes 
vulgare  (q.  v.)  were  used,  was  due  probably  to  the  fact  that  more 
inoculations  were  made  on  each  host  and  more  spores  used.  In 
general  the  species  inoculated  from  these  two  hosts  corresponded 
quite  closely  in  results  obtained.  Altogether  eighty  inoculations 
were  made  from  R.  nigrum,  of  which  thirty-three  or  41%  were 
successful,  which  is  lower  than  from  Rihes  vulgare,  but  the  number 
of  sori  produced  was  greater  than  with  the  latter  host. 

II  stage  from  Ribes  nigrum:  on  Parnassia  caroliniana,  565,  0.3,  '18, 
failed:  on  Ribes  alpestre,  375,  S.  13,  '18,  failed;  526,  S.  28,  '18,  failed; 
1038,  Au.  6,  '19,  failed;  1061,  Au.  13,  '19,  failed:  on  R.  alpinum  9,  428, 
S.  17,  '18,  fair,  II,  III:  on  R.  alpinum d',  376,  S.  13,  '18,  failed;  523,  S.  28, 
'18,  failed;  1030,  Au.  6, '19,  failed;  1059,  Au.  13, '19,  failed:  on  R.  ameri- 
canum, 374,  S.  13,  '18,  fair,  II,  III;  1047,  Au.  7,  '19,  failed;  1057,  Au.  13, 
'19,  failed:  on  R.  aureum,  1040,  Au.  7,  '19,  failed;  1065,  Au.  13,  '19, 
failed:  on  R.  aureum  chrysococcum,  392,  S.  13,  '18,  good,  II,  III;  398, 
S.  14,  '18,  failed;  527,  S.  28,  '18,  failed;  1043,  Au.  7,  '19,  failed;  1068, 
Au.  13,  '19,  failed:  on  R.  caucasicmn,  381,  S.  13,  '18,  failed;  524,  S.  28, 
'18,  failed;  1032,  Au.  6,  '19,  failed:  on  R.  curvatum.,  380,  S.  13,  '18,  failed; 
529,  S.  28,  '18,  failed;  1051,  Au.  7,'19,  failed;  1056,  Au.  13,  '19,  failed: 
on  R.  Cynosbati,  377,  S.  13,  '18,  good,  II;  396,  S.  14,  '18,  good,  II;  1041, 
Au.  7,  '19,  poor,  II:  on  R.  Cynosbati  inerme,  397,  S.  14,  '18,  poor,  II; 
1036,  Au.  6,  '19,  fair,  II:  on  R.  diacantha,  429,  S.  17,  '18,  failed:  on  R. 
divaricatum^,  379,  S.  13,  '18,  good,  II;  1037,  Au.  6,  '19,  failed:  on  R. 
fasciculaium  chinense,  399,  S.  14,  '18,  good,  II:  on  R.  Grossularia,  1033, 
Au.  6,  '19,  failed:  on  R.  Grossularia  (uva-crispa),  382,  S.  13,  '18,  fair,  II: 
on  R.  giraldii,  378,  S.  13,  '18,  failed;  528,  S.  28,  '18,  failed;  1053,  Au.  7, 
'19,  failed;  1067,  Au.  13,  '19,  failed:  on  R.  hirtellum,  383,  S.  13,  '18, 
good,  II,  III;  1049,  Au.  7,  '19,  failed:  on  R.  holosericeum,  384,  S.  13,  '18, 
failed;  525,  S.  28,  '18,  failed;  1048,  Au.  7,  '19,  fair,  II,  III;  1063,  Au.  13, 
'19,  failed:  on  R.  intermedium,  385,  S.  13,  '18,  good,  II,  III;  1044,  Au.  7, 
'  19.  fair,  II:  on  R.  longiflorum,  400,  S.  14,  '18,  fair,  II,  III:  on  R.  luridum, 
386,  S.  13,  '18,  good,  II,  III;   1046,  Au.  7,  '19,  failed:    on  R.  nigrum,  387, 


PLATE  XXVI 


b.     Callus  on  petiole  of  Ribes 
nigrum,  p.  480. 


a.     II  stage  of  Cronartium  Comptoniae  on 
Myrica  asplenifolia,  pp.  479,  484. 


c.     II  stage  of  Cronartium  ribicola  on  Ribes 
nigrum,  p.  485. 


d.     Roots  from  callus  on  SoH- 
dago  rugosa,  p.  480. 


ARTIFICIAL  INOCULATIONS  IN   PETRIE  DISHES. 


DETAILS    OF   INOCULATIONS   AND    INFECTIONS  489 

S.  13,  '18,  good,  II,  III;  997,  Jl.  12,  '19,  fair,  II;  1069,  Au.  5,  '19,  excellent, 
II,  III:  on  R.  nigrimi  aconitifolium,  388,  S.  13,  '18,  good,  II,  III;  1035, 
Au.  6,  '19,  fair,  II,  III;  1058,  Au.  13,  '19.  fair,  II:  on  R.  oxyacanthoides, 
395,  S.  13,  '18,  good,  II,  III:  on  R.  robustum,  391,  S.  13,  '18,  good,  II, 
III;  1031,  Au.  6,  '19,  poor,  II;  1064,  Au.  13,  '19,  fair,  II,  III:  on  R. 
stenocarpum,  390,  S.  13,  '18,  failed;  522,  S.  28,  '18,  failed;  1045,  Au.  7,  '19, 
failed;  1062,  Au.  13,  '19,  failed:  on  R.  tenue,  389,  S.  13,  '18,  good,  II, 
III;  1042,  Au.  7,  '19,  failed;  1060,  Au.  13,  '19,  failed:  on  R.  vulgare,  394, 
S.  13,  '18,  fair,  II,  III:  on  R.  vulgare  (white  currant),  1050,  Au.  7,  '19, 
failed:  on  Ribes  sp.  (large  gooseberry),  1052,  Au.  7,  '19,  failed:  on  Ribes 
sp.  (Smith's  small  gooseberry),  393,  S.  13,  '18,  fair,  II,  III;  1034,  Au.  6, 
'19,  failed;    1066,  Au.  13,  '19,  failed. 

II  from  Ribes  nigrian  (Petri  dish):  on  R.  nigrum,  366,  Je.  26,  '18, 
good.  II;  508,  S.  25,  '18,  poor.  III;  645,  D.  9,  '18,  failed;  1027,  Jl.  28 
'19,  fair,  II. 

Inoculations  with  II  stage  from  Ribes  vulgare.  In  this  series  the 
II  spores  were  all  from  Ribes  vulgare  and  successful  inoculations 
were  made  on  the  following  hosts:  Rihes  americanum,  R.  Cynos- 
hati,  R.  Cynoshati  inerme,  R.  fasciculatum  chinense,  R.  Grossularia 
(uva-crispa) ,  R.  hirtellum,  R.  intermedium,  R.  longiflorum,  R. 
luridum,  R.  nigrum,  R.  nigrum  aconitifolium,  R.  orientate,  R.  oxy- 
acanthoides, R.  rohustum,  and  Rihes  sp.  (Smith's  small  gooseberry). 
The  best  results  were  obtained  with  ^.  Cynoshati,  R.  longiflorum, 
R.  nigrum,  and  R.  oxyacanthoides.  Of  the  twenty-seven  inocula- 
tions made  fifteen,  or  56%,  were  successful.  All  the  inoculations, 
except  the  last  two,  were  made  on  Sept.  17,  1918. 

II  stage  from  Ribes  vulgare:  on  R.  alpestre,  402,  failed:  on  R.  alpinum 
9,  427,  failed:  on  R.  alpinum  d',  403,  failed:  on  R.  a7nericanum,  401, 
poor,  II:  on  R.  aureum  chrysococcum,  420,  failed:  on  R.  caucasicum, 
405,  failed:  on  R.  curvatum,  409,  failed:  on  R.  Cynosbati,  404,  good,  II: 
on  R.  Cynosbati  inerme,  406,  poor,  II:  on  R.  fasciculatum  chinense,  421, 
poor,  II:  on  R.  Grossularia  {uva-crispa),  410,  poor,  II,  III:  on  R. 
giraldii,  407,  failed:  on  R.  hirtellum,  412,  poor,  II:  on  R.  holosericeum, 
411,  failed:  on  R.  intermedium,  413,  poor,  II,  III:  on  R.  longiflorum, 
425,  good,  II,  III:  on  R.  luridum,  414,  poor,  II,  III:  on  R.  nigrum,  415, 
good,  II,  III:  on  R.  nigrum  aconitifolium,  4i6,  poor,.  II,  III:  on  R. 
orientale,  422,  poor,  II:  on  R.  oxyacanthoides,  426,  good,  II:  on  R.  ro- 
bustum, 417,  poor,  II,  III:  on  R.  stenocarpum,  418,  failed:  on  R.  tenue, 
419,  failed:  on  R.  vulgare,  424,  failed;  998  (Fay's  Prolific),  Jl.  12,  '19,  failed: 
on  Ribes  sp.  (Smith's  small  gooseberry),  423,  S.  17,  '18,  poor.  III. 

Inoculations  with  II  stage  from  Rihes  sps.  The  host  species 
from  which  the  II  spores  were  obtained  are  uncertain  but  the 
results  were  quite  successful  in^each  case. 

II  from  Ribes  sp.:  on  R.  nigrum,  299,  My.  27,  '18,  good,  II;  329,  Je.  3, 
'18,  good,  II;  331,  Je.  5,  '18,  excellent,  II,  III:  on  R.  vulgare,  300,  My. 
27,  '18,  good,  II. 

Inoculations  from  III  stage.  There  was  no  indication  from  these 
experiments  that  the  III  stage  from  Rihes  could  re-inoculate  Rihes. 
When  tried  on  pine  leaves,  however,  the  results  were  successful 
in  one  case  where  the  juvenile-form  leaves  were  still  attached  to  a 
young  shoot.    Results  as  a  rule  are  not  to  be  expected  even  here  as 


490  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   260. 

no  sign  of  infection  is  usually  visible  for  a  month  or  two  after  inocu- 
lation. In  the  successful  case  reported  there  was  a  slight  golden- 
yellow  spotting  thirty-eight  days  after  inoculation  and  sections 
showed  the  characteristic  sclerotial  masses  present. 

Ill  stage  from  Ribes  nigrum:  on  Pinus  Strobus,  584  (stem  uncut),  0. 7,  '18, 
failed;  585  (stem  cut),  O.  7,  18,  failed;  589  (stems  uncut  and  buds),  O. 
8,  '18,  failed;  583  (leaves),  O.  7,  '18,  failed;  588,  O.  8,  '18,  goad,  (yellow 
spots  and  sclerotia):  on  Ribes  intermedium,  1112,  0.25  '19,  failed:  on 
R.  nigrum,  631,  O.  19,  '18,  failed;  1113,  O.  25,  '19,  failed. 

GymnoGonia  interstitialis  (Schl.)  Lagerh. 

Infections  from  the  I  stage  resulted  from  Ruhus  allegheniensis 
on  R.  allegheniensis  and  R.  villosus;  from  R.  hispidus  on  R. 
hispidus  and  R.  villosus;  from  R.  occidentalis  on  R.  hispidus; 
from  R.  villosus  on  R.  hispidus  and  R.  villosus.  The  III  stage  ap- 
peared in  all  cases.  Only  ten  out  of  forty-six  infections,  or  22% 
were  successful.  This  low  rate  is  due  in  part  to  the  leaves  not 
keeping  in  good  condition  long  enough  to  secure  results,  as  it 
takes  some  time  for  the  sori  to  mature. 

I  stage  from  Rubus  allegheniensis  (R.  villosus):  on  R.  allegheniensis 
(wild),  1357,  Je.  30,  '20,  fair,  III:  on  R.  villosus,  336,  337,  Je.  6,  '18, 
failed;    1358,  Je.  30,  '20,  good,  III. 

I  stage  from  Rubus  hispidus:  on  R.  hispidus,  4302,  Je.  2,  '23,  fair.  III; 
4340,  Je.  15,  '23,  failed:  on  R.  villosus,  338,  339,  Je.  6,  '18,  failed;  959, 
Je.  11,  '19,  excellent.  III;  3087,  Je.  5,  '22,  failed;  4295,  Je.  1,  4203,  Je.  2, 
'23,  failed;  4341,  Je.  15,  '23,  good.  III:  on  Rubus,  sps.  (wild  and  cult, 
raspberry),  3084,  3085,  Je.  5,  '22,  failed;  4296,  Je.  1,  '23,  failed:  on 
Rubus  ep.  (cult,  blackberry),  3086,  Je.  5,  '22,  failed;  4294,  Je.  1,  '23, 
failed.     See  Plate  XXVb. 

I  stage  from  Rubus  occidentalis:  on  R.  allegheniensis,  1350  (wild), 
1354  (Erie),  1356,  (Snyder),  Je.  22,  '20,  failed;  3090  (cult.),  Je.  5,  '22, 
failed;  4310  (cult.),  Je.  8,  '23,  failed;  4353  (cult.),  Je.  20,  '23,  failed; 
4356,  Je.  20,  '23,  failed:  on  R.  hispidus,  4311,  Je.  8,  '23,  poor.  III;  4354, 
Je.  20,  '23,  failed;  4357,  Je.  20,  '23,  failed:  on  R.  occidentalis,  1346,  1352, 
Je.  22,  '20,  failed:  on  R.  villosus,  1348,  Je.  22,  '20,  failed;  3091,  Je.  5,  '22, 
failed;  4309,  Je.  8,  '23,  failed;  4352,  Je.  20,  '23,  failed;  4355,  Je.  20,  '23, 
failed;  4581,  Jl.  2,  '24,  failed:  on  Rubus  sps.  (cult,  and  wild  raspberry), 
3088-89,  Je.  5,  '22,  failed. 

I  stage  from  Rubus  villosus  (R.  canadensis):  on  R.  allegheniensis, 
4326,  Je.  12,  '23,  failed;  on  R.  hispidus,  4338,  Je.  15,  '23,  excellent.  III: 
on  R.  villosus,  4325,  Je.  12,  '23,  poor.  III;  4339,  Je.  15,  '23,  failed;  4580, 
Jl.  2,  '24,  good.  III;   4585,  Jl.  10,  '24,  excellent.  III. 

I  stage  from  Rubus  sps.  (wild  raspberry):  on  R.  villosus,  960,  Je.  11, 
'19,  failed:    on  Rubus  sps.  970,  Je.  13,  '19,  faUed. 

Gymnosporangium. 

Of  the  five  species  tried  from  this  genus  we  were  successful  in 
securing  infections  with  only  two,  chiefly  because  the  wrong  host 
or  the  O  stage  was  used  with  the  other  three.  Altogether  thirty- 
nine  tests  were  made  of  which  fourteen  or  36%  were  successful. 
With  G.  Juniperi-virginianae,  where  more  likely  hosts  were  used, 


DETAILS   OF   INOCULATIONS  AND   INFECTIONS  491 

46%  of  the  inoculations  were  successful.  With  Gymnosporangiuni 
successful  results  in  Petri  dishes  are  to  be  expected  only  with  the 
III  stage  and  with  this  only  the  O  stage  appears  since  the  length 
of  time  to.  develop  the  I  stage  is  too  great  to  keep  the  leaves  alive. 

Gymnosporangium  clavariaeforme  (Jacq.)  DC. 

This  failure  is  probably  due  to  the  use  of  the  wrong  host,  as 
Pyrus  is  not  given  by  Kern  (N.  A.  F.)  as  one  for  this  species  which 
usually  occurs  on  Amelanchier  sps.,  and  Cydonia  vulgaris,  both 
hosts  in  Connecticut. 

Ill  stage  from  Juniperus  communis:  on  Pyrus  ioensis  (Bechtel's  Fl. 
Crab),  923,  My.  27,  '19,  failed. 

Gymnosporangium  clavipes  Ck.  &  Pk. 

The  usual  hosts  for  this  species  are  Amelanchier,  Crataegus  and 
Cydonia,  although  Kern  (N.  A.  F.)  gives  Pyrus  Malus  as  a  host 
from  Massachusetts.  Pyrus,  however,  does  not  seem  to  be  a  very 
susceptible  host  from  our  results. 

O  stage  from  Amelanchier  sp.:     on  Pyrus  ioensis,  936,  Je.  6,  '19,  failed. 

Ill  stage  from  Juniperus  virginiana:  on  Pyrus  ioensis  (Bechtel's  Fl. 
Crab)  922,  My.  27,  '19,  failed:  on  P.  Malus  (Wealthy)  811,  My.  20,  '19, 
failed. 

Gymnosporangium  cornutum  (Pers.)  Arth. 

As  in  all  species  tried  no  results  were  obtained  from  inoculations 
with  the  O  stage.  This  rust,  however,  has  not  been  listed  on  the 
hosts  tried  here  so  the  results  do  not  mean  so  much  as  if  Sorhus 
had  been  used. 

O  stage  from  Sorbus  americana:  on  Crataegus  crus-galli,  967,  Je.  12,  '19, 
failed:  on  Pyrus  ioensis,  968,  Je.  12,  '19,  failed:  on  P.  Malus  (Wealthy), 
969,  Je.  12,  '19,  failed. 

Gymnosporangium  Juniperi-virginianae  Schw. 

Here  inoculations  with  the  0  stage  were  made  on  hosts  known 
to  be  very  susceptible  but  without  results  which  seems  to  indicate 
that  the  0  stage  is  not  a  means  of  spreading  the  rust.  Inoculations 
with  the  III  stage  were  successful  on  Pyrus  ioensis  and  P.  Malus 
only,  the  other  species,  Pyrus  communis  and  Cydonia  vulgaris,  not 
being  reported  as  hosts  for  this  species  by  Kern.  All  three  inocu- 
lations took  on  the  Bechtel's  Flowering  Crab  which  is  a  very 
susceptible  species.  On  Pyrus  Malus,  however,  the  results  varied 
with  the  different  varieties  used,  failing  on  Baldwin,  Gravenstein, 
Mcintosh  and  Northern  Spy,  taking  poorly  on  Fall  Pippin, 
Greening,  King  and  Sutton's  Beauty,  and  taking  well  on  Duchess 
of  Oldenburg,  Hurlburt,  Russet  and  Wealthy.  These  results 
agree  well  with  the  observations  we  have  made  on  these  varieties 


492  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   260. 

in  nature.  The  Petri  dish  method  seems  to  be  a  very  easy  way  to 
test  the  susceptibility  of  different  varieties  of  apples  to  these  rusts. 
Of  the  inoculations  with  the  III  stage  52%  were  successful. 

0  stage  from  Pyrus  Malus:  on  Pyrus  ioensis,  953,  Je.  9,  '19,  failed:  on 
Pyrus  Mains  (Wealthy),  954,  Je.  9,  '19,  failed;  4030-32  (young  and  old 
leaves),  Je.  20,  '22,  failed. 

1  stage  from  Pyrus  Malus:  on  Juniperus  virginiana,  1029,  Au.  5,  '19, 
failed. 

Ill  stage  from  Juniperus  virginiana:     on  Cydonia  vulgaris,  801,  My. 

19,  '19,  failed;  940,  Je.  7,  '19,  failed:  on  Pyrus  communis,  800,  My.  19, 
'19,  failed;  938  (Seckel),  Je.  7,  '19,  failed;  939,  Je.  7,  '19,  failed:  on  P. 
ioensis  (Bechtel's  Fl.  Crab),  799,  My.  19,  '19,  excellent,  O;  924,  My.  27, 
'19,  poor,  O;  937,  Je.  7,  '19,  good,  O;  4306,  Je.  7,  '23,  excellent,  O:  on  P. 
Malus,  798,  My.  19,  '19,  failed;  810  (Baldwin),  My.  20,  '19,  failed;  942 
(Baldwin),  Je.  7,  '19,  failed;  943  (Duchess  of  Oldenberg),  Je.  7,  '19, 
good,  O;  941  (Fall  Pippin),  Je.  7,  '19,  poor,  O;  946  (Gravenstein),  Je.  7, 
'19,  failed;  952  (Greening),  Je.  7,  '19,  poor,  O;  950  (Hulbert),  Je.  7,  '19, 
good,  O;  946  (King),  Je.  7,  '19,  poor,  O;  947  (Mcintosh),  Je.  7,  '19, 
failed;  944  (Northern  Spy),  Je.  7,  '19,  failed;  951  (Russet),  Je.  7,  '19, 
good,  O;   948  (Sutton's  Beauty),  Je.  7,  '19,  poor,  O;   809  (Wealthy),  My. 

20,  '19,  good,  O;    949  (Wealthy),  Je.  7,  '19,  poor,  O.     See  Plate  XXVc. 

Gymnosporangium  nidus-avis  Thaxt. 

Successful  inoculations  were  made  with  this  species  only  on 
Quince  (Cydonia  vulgaris)  and  the  Wealthy  apple,  failing  on  the 
other  varieties  of  Pyrus  Malus,  the  Pear  and  Bechtel's  Crab. 
Wealthy  is  one  of  the  most  susceptible  varieties  of  apples  to  Gy7n- 
nosporangium  Juniperi-virginianae  but  Kern  (N.  A.  F.  7^:  196.) 
does  not  list  Pyrus  Malus  as  a  host  for  G.  nidus-avis  and  it  may  be 
that  in  nature  it  does  not  attack  the  apple. 

Ill  stage  from  Juniperus  virginiana:  on  Cydonia  vulgaris,  805,  My.  19, 
'19,  fair,  O:  on  Pyrus  communis,  804,  My.  19,  '19,  failed:  on  P.  ioensis, 
803,  My.  19,  '19,  failed:  on  P.  Malus,  802,  My.  19,  '19,  failed;  813 
(Baldwin),  My.  20,  '19,  failed;    812  (Wealthy),  My.  20,  '19,  fair,  O. 

Kuehneola  alhida  (Kuehn)  Magn. 

Only  two  inoculations  out  of  nine  were  successful  with  this 
species,  taking  from  Rubus  allegheniensis  and  R.  hispidus  on  the 
same  species.  This  seems  too  low  considering  the  hosts  and 
character  of  the  spore  material  used,  but  perhaps  the  lateness  of 
the  season  with  some  of  the  inoculations  explains  their  failure. 

II  stage  from  Rubus  allegheniensis:  on  R.  allegheniensis,  1070,  S.  9,  '19, 
poor,  II:  on  R.  villosus,  1071,  S.  9,  '19,  failed:  on  Rubus  sp.  (raspberry), 
1072,  S.  9,  '19,  failed. 

II  stage  from  Rubus  hispidus:  on  R.  hispidus,  4298,  Je.  1,  '23,  fair,  II: 
R.  villosus,  4297,  Je.  1,  '23,  failed. 

II  stage  from  Rubus  villosus:    on  R.  villosus,  4621,  S.  16,  '24,  failed. 

II  stage  from  Rubus  sp.  (wild  blackberry),  on  R.  allegheniensis,  1546, 
N.  10,  '20,  failed:  on  R.  villosus,  1545,  N.  10,  '20,  failed:  on  Rubus  sp. 
(cult,  raspberry),  1547,  N.  10,  '20,  failed. 


DETAILS    OF   INOCULATIONS   AND   INFECTIONS  493 

Melampsora  sps. 

We  have  carried  on  a  considerable  number  of  inoculations  with 
Melampsora  species  from  Populus  and  Salix  on  various  species  of 
Betula,  Populus  and  Salix.  Uniform  failure  to  inoculate  Betula, 
on  both  trees  and  in  Petri  dishes,  has  eliminated  the  rust  on  that 
host  from  consideration,  on  infectional  as  well  as  on  morphological 
grounds,  as  stated  subsequently  under  Melampsoridium.  The 
only  reason  for  making  these  inoculations  was  the  frequent  associa- 
tion of  the  Betula  rust  with  those  on  Populus  and  Salix. 

Examining  our  Connecticut  herbarium  specimens  on  Populus 
and  Salix.  we  find  that  there  are  slight  morphological  characters 
that  apparently  separate  them  into  four  species,  two  on  Salix  and 
two  on  Populus.  Yet  we  are  not  sure  whether  these  might  not  be 
more  satisfactorily  combined  in  fewer  species.  Our  inoculations 
have  also  given  conflicting  results,  II  spores  from  both  Populus 
grandidentata  and  P.  tremuloides  having  apparently  infected  leaves 
of  Salix;  also  II  spores  from  Popidus  tremidoides  took  on  P.  gran- 
didentata but  not  from  the  latter  on  the  former,  while  II  spores 
from  Salix  sp.  failed  on  both  the  poplars.  The  rusts  on  these  three 
hosts  have  been  found  associated  in  the  same  locality  with  Caeoma 
Ahietis-canadensis  and  their  II  stages  are  very  similar.  All  these 
observations  have  caused  us  to  question  whether  we  were  dealing 
with  three  or  one  species.    See  notes  under  each. 

Melampsora  Ahietis-canadensis  (Farl.)  Ludw. 

The  inoculations  with  the  I  stage  {Caeoma  Ahietis-canadensis) 
from  Tsuga  canadensis  took  in  all  the  tests  (except  possibly  one) 
on  Populus  grandidentata  and  failed  on  Betula  and  Salix  sps.  and 
on  all  the  other  species  of  Populus  except  one  doubtful  sorus  on 
P.  tremuloides,  the  other  two  trials  on  this  host  failing  though 
taking  at  the  same  time  on  P.  grandidentata.  The  inoculations 
with  the  II  stage  from  Popidus  grandidentata  were  uniformly 
failures,  even  on  P.  grandidentata,  except  the  very  suspicious  infec- 
tion on  Salix  sp.  which  leaves  possibly  were  already  infected,  as 
the  first  sori  appeared  within  five  days  after  inoculation. 

I  stage  from  Tsuga  canadensis:  on  Betula  sp.,  4010,  Je.  17,  '22,  failed: 
on  Populus  alba,  4009,  Je.  16,  '22,  failed;  4014,  Je.  17,  '22,  failed:  on  P. 
deltoides,  3096,  Je.  15,  '22,  failed:  on  P.  grandidentata,  3094,  Je.  15,  '22, 
fair,  II;  4011,  Je.  17,  '22,  poor,  II;  4021,  Je.  19,  '22,  failed?;  4586,  Jl.  10, 
'24,  poor,  II:  on  P.  nigra  italica,  3093,  Je.  15,  4013,  Je.  17,  '22,  failed: 
on  P.  tremuloides,  3095,  Je.  15,  '22,  poor,  II  (one  sorus);  4012,  Je.  17,  '22, 
failed;  4587,  Jl.  10,  '24,  failed:  on  Salix  sps.,  4401-2,  Je.  15,  '22,  failed; 
4015-18,  Je.  17,  '22,  failed;    4022-29,  Je.  19,  '22,  failed. 

II  stage  from  Populus  grandidentata:  on  Betula  Lenta,  557,  O.  2,  '18, 
failed:  on  B.  populifolia,  554,  O.  2,  '18,  failed:  on  Populus  deltoides, 
1510,  O.  28,  '20,  failed:  on  P.  grandidentata,  560,  O.  2,  '18,  failed;  1498, 
O.  27,  '20,  failed;  1500,  O.  28,  '20,  failed:  on  P.  tremuloides,  563,  O.  2, 
'18,  failed;  1497,  O.  27,  '20,  failed:  on  Salix  sp.  (New  Haven),  1501, 
O.  28,  '20,  fair,  II. 


494  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   260. 

Melampsora  americana  Arth. 

The  II  stage  from  Salix  sps.  failed  on  the  three  species  of  Betula 
and  the  six  of  Populus  that  were  inoculated.  It  also  failed  on 
certain  species  of  Salix  but  took  on  others,  six  of  the  twelve  inocu- 
lations being  successful. 

II  stage  from  Salix  sp:  on  Betula  alba  papyrifera,  448,  S.  20,  '18, 
failed:  on  B.  lenta,  449,  S.  20,  '18,  failed;  1451,  O.  14,  '20,  failed;  1489, 
O.  27,  '20,  failed;  1512,  O.  28,  '20,  failed:  on  B.  popuUfoUa,  450,  S.  20, 
'18,  failed;  1450,  0.14,  '20,  failed;  1490,  O.  27,  '20,  failed;  1513,  O.  28, 
'20,  failed:  on  Populus  alba,  451,  S.  20,  '18,  failed;  1509,  O.  28,  '20, 
failed;  1519,  O.  28,  '20,  failed:  on  P.  balsamifera,  452,  S.  20,  '18,  failed: 
on  P.  deltoides,  453,  S.  20,  '18,  failed;  1504,  O.  28,  '20,  failed;  1520,  O. 
28,  '20,  failed:  on  P.  grandidentata,  454,  S.  20,  '18,  failed;  1449,  O.  14, 
'20,  failed;  1492,  O.  27,  '20,  failed;  1507,  1517,  O.  28,  '20,  failed:  on  P. 
nigra  italica,  455,  S.  20,  '18,  failed;  1508,  1518,  O.  28,  '20,  failed:  on  P. 
trermdoides,  456,  S.  20,  '18,  failed;  1448,  O.  14,  '20,  failed;  1491,  O.  27, 
'20,  failed;  1506,  1516,  O.  28,  '20,  failed:  on  Salix  amygdalina  (3),  484, 
S.  21,  '18,  poor,  II;  495,  S.  21,  '18,  failed:  on  S.  amygdalina  americana 
(2),  494,  S.  21,  '18,  failed:  on  S.  pentandra  (5,  Lemley),  497,  S.  21,  '18, 
poor,  II;  1502,  1514,  O.  28,  '20,  failed;  on  S.  purpurea  (1  and  4),  493, 
496,  S.  21,  '18,  failed;  on  Salix  sp.  (New  Haven),  1447,  O.  14,  '20,  poor, 
II;  1503,  O.  28,  '20,  good,  II;  1505,  O.  28,  '20,  poor,  II;  1515,  O.  28,  '20, 
poor,  II. 

Melampsora  Medusae  Thuem. 

The  inoculations  with  the  II  stage  from  Populus  tremuloides  on 
the  same  host  took  in  good  shape  in  three  out  of  the  four  trials 
and  failed  on  all  the  other  species  of  Populus,  Betula  and  Salix, 
except  apparently  in  one  case  on  Populus  grandidentata  and  one 
on  Salix  sp.  made  at  the  same  time  and  with  same  material  that 
took  on  P.  tremuloides.  This  means  either  that  these  two  latter 
hosts  were  already  infected  when  used  or  else  that  all  three  hosts 
are  inhabited  by  the  same  species  and  not  by  three  different  ones 
as  considered  here. 

II  stage  from  Populus  tremuloides:  on  Betula  alba,  430,  S.  20,  '18, 
failed:  on  Betula  lenta,  431,  S.  20,  '18,  failed;  558,  O.  2,  '18,  failed;  1461, 
O.  14,  '20,  failed:  on  B.  popidifolia,  432,  S.  20,  '18,  failed;  555,  O.  2,  '18, 
failed;  1460,  O.  14,  '20,  failed:  on  Populus  alba,  433,  S.  20,  '18,  failed: 
on  P.  balsamifera,  434,  S.  20,  '18,  failed:  on  P.  deltoides,  435,  S.  20,  '18, 
failed:  on  P.  grandidentata,  436,  S.  20,  '18,  failed;  561,  O.  2,  '18,  failed; 
1459,  O.  14,  '20,  good.  III:  on  P.  nigra  italica,  437,  S.  20,  '18,  failed: 
on  P.  tremuloides,  438,  S.  20,  '18,  good,  II;  465,  S.  20,  '18,  fair,  II-III; 
564,  O.  2,  '18,  failed;  1458,  O.  14,  '20,  good,  II:  on  Salix  amygdalina  (3), 
505,  S.  21,  '18,  failed:  on  S.  amygdalina  americana  (2),  504,  S.  21,  '18, 
failed:  on  S.  pentandra  (5),  507,  S.  21,  '18,  failed:  on  S.  purpurea  (1), 
503,  S.  21,  '18,  failed:  S.  purpurea  (4),  506,  S.  21,  '18,  failed:  on  Salix  sp. 
(New  Haven),  1457,  O.  14,  '20,  poor,  II. 

Melampsoridium  hetulinum  (Pers.)  Kleb. 

All  six  inoculations  with  the  I  stage  failed,  but  only  one  was 
made  on  Betula  species.  Only  18%  of  the  thirty-three  inocula- 
tions with  the  II  stage  was  successful  also  for  the  reason  that  many 


DETAILS   OF   INOCULATIONS   AND    INFECTIONS  495 

of  them  were  made  on  Populus  and  Salix.  In  this  state  rusts  on 
Populus,  Salix  and  Betula  often  occur  together  and  it  was  thought 
that  possibly  there  might  be  some  connection  between  them  not 
yet  discovered.  As  far  as  Betula  is  concerned  both  from  these 
experiments  and  microscopical  examination  of  the  II  stage  found 
on  it,  there  is  but  one  species  of  rust  and  it  does  not  occur  on  either 
Populus  or  Salix.  If  we  consider  only  the  inoculation  from 
Betula  sps.  to  Betula  sps.,  the  results  are  better,  since  38%  of  these 
was  successful.  The  favorable  inoculations  with  the  II  stage  were 
as  follows:  from  Betula  popuUfolia  on  B.  lenta  and  B.  populifoUa. 
In  the  case  of  spores  from  B.  lenta  on  these  two  hosts  the  results 
were  negative  probably  because  the  nmnber  of  inoculating  spores 
was  small. 

I  stage  from  Larix  americana:  on  Betula  sp.,  4316,  Je.  8,  '23,  failed: 
on  Populus  deltoides,  4314,  Je.  8,  '23,  failed:  on  P.  grandidentata,  4312,  Je. 
8,  '23,  failed:  on  P.  nigra  italica,  4313,  Je.  8,  '23,  failed:  on  Salix  sp., 
4305,  Je.  7,  4315,  Je.  8,  '23,  failed. 

II  stage  from  Betula  lenta:  on  B.  lenta,  1485,  O.  27,  '20,  failed:  on 
B.  populifoUa,  1486,  O.  27,  '20,  failed:  on  Populus  grandidentata,  1488, 
O,  27,  '20,  failed:    on  P.  tremuloides,  1487,  O.  27,  '20,  failed. 

II  stage  from  Betula  populifoUa:  on  B.  alba  papyrifera,  439,  S.  20,  '18, 
failed:  on  B.  lenta,  440,  S.  20,  '18,  failed;  556,  O.  2,  '18,  failed;  1456,  O.  14, 
'20,  poor,  II;  1493,  O.  27,  '20,  fair,  II:  on  B.  populifoUa,  441,  S.  20,  '18, 
fair,  II;  553,  O.  2,  '18,  failed;  1455,  O.  14,  '20,  failed;  1494,  O.  27,  '20, 
failed;  1499,  O.  28,  '20,  poor,  II;  1511,  O.  28,  '20,  poor,  II:  on  Populus 
alba,  442,  S.  20,  '18,  failed:  on  P.  balsamifera,  443,  S.  20,  '18,  failed:  on 
P.  deltoides,  444,  S.  20,  '18,  failed:  on  P.  grandidentata,  445,  S.  20,  '18, 
failed;  559,  O.  2,  '18,  failed;  14.54,  O.  14,  '20,  failed;  1496,  O.  27,  '20,  failed: 
on  P.  nigra  italica,  446,  S.  20,  '18,  failed:  on  P.  tremuloides,  447,  S.  20,  '18, 
failed;  562,  O.  2,  '18,  failed;  1453,  O.  14,  '20,  failed;  1495,  O.  27,  '20, 
failed:  on  Salix  amygdalina  (3),  500,  S.  21,  '18,  failed:  on  S.  amygda- 
lina  americana  (2),  499,  S.  21,  '18,  failed:  on  S.  purpurea  (1),  498,  S.  21,  '18, 
failed:  on  S.  purpurea  (4),  501,  S.  21,  '18,  failed:  on  S.  pentandra  (5), 
502,  S.  21,  '18,  failed:    on  Salix  sp.,  1452,  O.  14,  '20,  failed. 

Melampsoropsis  Cassandrae  (Pk.  &  Clint.)  Arth, 

The  results  in  this  case  are  interesting  since  they  confirm  results 
obtained  with  plants  in  crocks,  namely  that  Picea  mariana  and 
P.  rubra  are  susceptible  hosts  for  producing  the  O  and  I  stages  of 
this  rust,  while  P.  excelsa  is  not.  The  inoculations  in  the  Petri 
dishes  were  made  on  leaves  still  attached  to  small  branches  and  the 
0  stage  with  pycniospores  only  appeared,  the  I  stage  appearing  on 
the  plants  in  the  crocks. 

III  stage  from  Cassandra  calyculata:  on  Picea  excelsa,  347,  Je.  8,  '18, 
failed;  925,  My.  27,  '19,  failed:  on  P.  mariana,  956,  Je.  11,  '19,  fair,  O:  on 
P.  rubra,  972,  Je.  14,  '19,  fair,  O. 

Melampsoropsis  Pyrolae  (D.C.)  Arth. 

This  rust  apparently  winters  over  here  through  the  II  stage,  as 
the  I  stage  has  not  been  found.     It  is  not  evident  why  the  two 


496  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   260. 

inoculations  with  the  II  stage  failed  since  the  leaves  remained  alive 
and  healthy  in  the  Petri  dishes  for  a  long  time,  and  the  spores  seem- 
ed in  good  condition  when  used. 

II  stage  from  Pyrola  americana:  on  P.  americana,  4301,  Je.  2,  '23, 
failed:    on  P.  ellipHca,  4300,  Je.  2,  '23,  failed. 

Phragmidium  Potentillae  (Pers.)  Karst. 

Inoculations  were  successful  in  two  out  of  the  three  tests  of  the 
II  stage  on  Potentilla  canadensis  on  the  same  host.  The  other 
attempts  were  made  on  plants  known  not  to  be  the  proper  hosts. 

II  stage  from  Potentilla  canadensis:  on  Betula  populifolia,  569,  O.  3,  '18, 
failed:  on  Populus  (;randidentata,  568,  O.  3,  '18,  failed:  on  P.  tremuloides, 
567,  O.  3,  '18,  failed:  on  Potentilla  canadensis,  566,  O.  3,  '18,  failed; 
996,  Jl.  12,  '19,  poor,  II;  1014,  Jl.  19,  '19,  fair,  II;  1014,  II,  a-b,  Au.  5, 
'19,  (a)  excellent,  II,  (b)  failed.     See  Plate  XXVa. 

Phragmidium  suhcorticium  (Schr.)  Wint. 

With  this  species  five  out  of  the  nine  inoculations  on  Rosa 
species  were  successful.  The  failures  seem  to  indicate  that  they 
were  on  varieties  that  were  at  least  somewhat  resistant  to  the  rust. 

II  stage  from  Rosa  sp.  (cult.):  on  Rosa  rugosa,  987,  Jl.  12,  '19,  failed: 
on  Rosa  sp.  (The  Farquhar),  993,  Jl.  12,  '19,  failed:  on  Rosa  sp.  (Ayrshire), 
989,  Jl.  12,  '19,  failed:  on  Rosa  sp.,  992,  Jl.  12,  '19,  poor,  II:  on  Rosa  sp. 
(Frau  Karl  Druschki's  hybrid  perpetual), 994,  Jl.  12, '19,  poor,  II:  on  Rosa 
sp.  (Madame  Plantier),  991,  Jl.  19,  '19,  poor,  II:  on  Rosa  sp.  (white),  990, 
Jl.  12.  '19,  poor,  II:   on  Rosa  sp.  (Wichuraina),  988,  Jl.  12,  '19,  failed. 

II  stage  from  Rosa  sp.  (Madame  Plantier,  Petri  dish  culture  991): 
on  Rosa  sp.  (Madame  Plantier),  1025,  Jl.  25,  'io,  poor,  II. 

Puccinia  sps. 

We  can  discuss  the  results  of  inoculation  with  species  of  Puccinia 
altogether  as  the  number  of  inoculations  with  most  of  them  were 
too  few  to  draw  any  special  conclusions.  In  fact  the  work  with 
Puccinia,  as  with  Uromyces,  was  chiefly  to  determine  how  success- 
ful the  Petri  dish  method  would  prove  for  those  species  of  rusts 
that  have  their  hosts  on  the  more  delicate  leaves  of  herbaceous 
plants,  many  of  which  are  also  of  such  size  that  they  have  to  be 
cut  before  they  can  be  placed  in  the  dish.  Of  the  forty-six  in- 
oculations 35%  was  successful  which  is  fair  considering  the 
difficulty  of  keeping  the  leaves  in  good  condition.  However,  even 
with  the  successful  ones,  the  amount  of  infection  was  not  usually 
very  abundant  and  often  the  sori  appeared  only  shortly  before  the 
leaves  died. 

Altogether  nineteen  species  of  Puccinia  were  tried  and  infection 
resulted  in  nine  as  follows.  Puccinia  Agropyri:  II  stage  from 
Agropyron  repens  on  A.  repens;  II  stage  from  Triticum  vulgar e  on 
Agropyron  repens.     Puccinia  coronata:  II  stage  from  Avena  saliva 


DETAILS    OF   INOCULATIONS   AND    INFECTIONS  497 

on  A.  sativa.  PuGcinia  graminis:  II  stage  from  Agrostis  alba  on 
A.  alba;  II  stage  from  Phleum  pratense  on  P.  pratense.  Puccinia 
ohsGura:  II  stage  from  Luzula  campestris  on  L.  campestris.  Puccinia 
Poarum:  II  stage  from  Poa  pratensis  on  P.  pratensis.  Puccinia 
Pruni-spinosae:  I  stage  from  Anemone  quinquefolia  on  Prunus 
serotina.  Puccinia  suaveolens:  II  stage  from  Cirsium  arvense  on 
C.  arvense.  Puccinia  Violae:  1  stage  from  Viola  hlanda  on  V. 
hlancla.  Puccinia  Thalictri:  III  stage  from  ThaUctrum  polygamum 
on  P.  polygamun.     (This  last  infection  is  considered  doubtful). 

Puccinia  Agropyri  Ell.  &  Ev. 

I  stage  from  ThaUctrum  polygamum:  on  Carex  sp.,  4332,  Je.  13,  '23, 
failed. 

II  stage  from  Agropyron  repens:  on  A.  repens,  1013,  Jl.  19,  '19,  poor,  II; 
1028,  Jl.  28,  '19,  failed;  4346,  Je.  16,  '23,  failed:  on  Panicum  sp.,  999,  Je.  12, 
'19,  failed. 

II  stage  from  Triticum  vulgare:   on  Agropyron  repeals,  1023,  Jl.  19,  '19, 
poor,  II. 

Puccinia  Andropogi  Schw. 

I  stage  from  Chelone  glabra:  on  Andropogon  scoparius,  4330,  Je.  13,  '23, 
fair,  II;    4342,  Je.  15,  '23,  failed. 

III  stage  from  Andropogon  scoparius:  on  Chelone  glabra,  4331,  Je. 
13,  '23,  failed. 

Puccinia  Anemones  Pers. 
Ill   stage  from  Anemone  quinquefolia  (poor  material):      on  ^4.  quinque- 
folia, 4321,  Je.  12,  '23,  failed:  on  ThaUctrum  sp.,  4320,  Je.  12,'23,  failed. 

Puccinia  Asparagi  DC. 

II  stage  from  Asparagus  officinalis:  on  A.  officinalis,  1055,  Au.  12, 
'19,  failed. 

Puccinia  coronata  Cda. 

II  stage  from  Avena  saliva:  on  A.  sativa,  581,  O.  7,  '18,  fair,  II;  632, 
0.  22,  '18,  good,  II,  III;  641,  O.  31,  '18,  poor,  II;  (II  stage  from  Petri 
dish  culture  632),  642,  O.  31,  '18,  poor,  II:  on  Secale  cereale,  633,  O.  22, 
'18,  failed. 

Puccinia  Ellisiana  Thuem. 

I  stage  from  Viola  sp. :  on  Andropogon  sp.,  4343,  Je.  15,  '23,  failed: 
on  Viola  sp.,  4334,  Je.  15,  '23,  failed. 

Puccinia  Eriophori  Thuem. 

I  stage  from  Senecio  aureus:  on  Eriophorum  viridi-carinalum,  4322, 
Je.  12,  '23,  failed. 

III  stage  from  Eriophorum  viridi-carinalum:  on  Senecio  aureus,  4324, 
Je.  12,  '23,  failed. 

Puccinia  Fraxinata  (Lk.)  Arth. 

I  stage  from  Fraxinus  americana:  on  Agropyron  repens,  1010,  Jl.  19, 
'19,  failed:  on  Fraxinus  americana,  1008,  Jl.  19,  '19,  failed:  on  Spariina 
patens  J uncea,  1003,  Jl.  18,  '19,  failed;  1005,  Jl.  19,  '19,  failed:  on  Spariina 
sp.  (large),  1002,  Jl.  18,  '19,  failed;    1004,  Jl.  19,  '19,  failed. 


498  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   260. 

PuGGinia  graminis  Pers. 

I  stage  from  Berberis  vulgaris:   on  Agrostis  alba,  4329,  Je.  13,  '23,  failed. 

II  stage  from  Agrostis  alba:   on  A.  alba,  1011,  Jl.  19,  '19,  poor,  II. 

II  stage  from  Phleum  pratense:  on  P.  pratense,  1012,  Jl.  19,  '19,  fair,  II. 

PuGcinia  MalvaGearum,  Mont. 

III  stage  from  Althaea  rosea:  on  A.  rosea,  995,  Jl.  12,  '19,  failed. 

Puccinia  ohscura  Schroet. 

II  stage  from  Luzula  campestris:  on  L.  campestris,  359,  Je.  21,  '18, 
failed;    934,  Je..  6, '19,  good,  II. 

PuGcinia  Poarum  Niels. 
II  stage  from  Poa  pratensis:  on  P.  pratensis,  1000,  Jl.  12,  '19,  poor,  II. 

Puccinia  Porri  (Sow.)  Wint. 

II  stage  from  Allium  cepa  (Egyptian):  on  A.  cepa  (garden),  1054,  Au. 
12,  '19,  failed. 

Puccinia  Pruni-spinosae  Pers. 

I  stage  from  Anemone  quinquefolia:  on  Prunus  persica,  4249,  My. 
19,  '23,  failed:  on  Prunus  serotina,  900,  My.  27,  '19,  poor,  II;  4250,  My. 
19,  '23,  excellent,  II:  on  Prunus  sp.  (cult,  plum),  4248,  My.  18,  '23, 
failed. 

Puccinia  ruhigo-vera  (DC.)  Wint. 

II  stage  from  Secale  cereale:  on  S.  cereale,  344,  Je.  8,  '18,  failed. 

Puccinia  suaveolens  (Pers.)  Rostr. 
II  stage  from  Cirsium  arvense:   on  C.  arvense,  1018,  Jl.  19,  '19,  fair,  II; 
1026,  Jl.  28,  '19,  poor,  II. 

Puccinia  Taraxaci  Plowr. 

II  stage  from  Taraxacum  officinale:  on  T.  officinale,  1001,  Jl.  14,  '19, 
failed  (leaves  decayed) ;    4345,  Je.  16,  '23,  failed. 

Puccinia  Thalictri  Chev. 

III  stage  from  Thalictrum  polygamum:  on  T.  polygamum,  4318,  Je.  12, 
'23,  good,  III  (telia  appeared  in  six  days  so  host  possibly  already  infected)? ; 
4347,  Je.  16,  '23,  failed. 

Puccinia  Violae  (Schum.)  DC. 
I  stage  from  Viola  blanda:  on  V.  blanda,  935,  Je.  6,  '19,  good,  II. 

Pucciniastrum  Myrtilli  (Schum.)  Arth. 

The  reason  the  I  stage  took  on  Gaylussacia  haccata  and  failed  on 
Vaccinium  vacillans  is  not  entirely  evident  since  the  latter,  ques- 
tionably, has  been  collected  as  host  for  the  II  and  III  stages  in  this 


DETAILS   OF   INOCULATIONS  AND   INFECTIONS  499 

state,  and  they  were  inoculated  under  apparently  identical  condi- 
tions. However,  the  Gaylussaoia  is  a  common  host  and  the  same 
year  the  inoculations  were  made  we  found  it  and  VacGinium 
pennsylvanicum  infected  together  in  a  locality  where  V.  vacillans 
was  entirely  free  though  close  to  the  other  infected  hosts. 

I  stage  from  Tsuga  canadensis:  on  Gaylussacia  baccata,  4020,  Je.  19, 
'22,  excellent,  II:  4041,  Jl.  19,  '22,  good,  II:  on  Vaccinium  vacillans,  4019, 
Je.  19,  '22,  failed;    4042,  Jl.  19,  '22,  failed. 

Uromyces  sps. 

Only  eight  inoculations  with  five  species  of  Uromyces  were  tried  and 
of  these  only  one  was  successful  as  follows.  Uromyces  Trifolii:  II  stage 
from  Trifolium  pratense  on  T.  pratense. 

Uromyces  Caladii  (Schw.)  Farl. 

I  stage  from  Arisaema  triphyllum:  on  A.  triphyllum,  4307,  Je.  8,  '23, 
failed. 

Uromyces  Caryophyllinus  (Schr.)  Wint. 

II  stage  from  Dianthus  Caryophyllinus:  on  D.  Carophyllinus,  646,  647, 
648,  649,  D.  27,  '18,  failed. 

Uromyces  houstoniatus  (Schw.)  Sheld. 
I  stage  from  Houstonia  caerulea:   on  Hypoxis  erecta,   4282,  My.  28,  '23, 
failed:    on  Luzula  campestris,  360,  Je.  21,  '18,  failed:    on  Sisyrinchium  sp., 
4299,  Je.  1,  '23,  failed. 

Uromyces  Lilii  (Lk.)  Fckl. 

I  stage  from  Lilium  sp.:    on  Lilium  sp.,  361,  Je.  21,  '18,  failed. 

Uromyces  Trifolii  (Hedw.)  Liro, 

II  stage  from  Trifolium  pratense:  on  T.  hybridum,  1017,  Jl.  19,  '19, 
failed:    on  T.  pratense,  1015,  Jl.  19,  '19,  poor,  II. 


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